diff --git a/plugins/ChannelDB.py b/plugins/ChannelDB.py
index ccb0944b0..709ed4e33 100644
--- a/plugins/ChannelDB.py
+++ b/plugins/ChannelDB.py
@@ -148,7 +148,7 @@ class ChannelDB(callbacks.PrivmsgCommandAndRegexp, ChannelDBHandler):
                                   actions=actions+%s""",
                            smileys, frowns, chars, words, int(isAction))
             try:
-                name = ircdb.users.getUserName(msg.prefix)
+                name = ircdb.users.getUser(msg.prefix).name
             except KeyError:
                 return
             cursor.execute("""SELECT COUNT(*)
@@ -181,7 +181,7 @@ class ChannelDB(callbacks.PrivmsgCommandAndRegexp, ChannelDBHandler):
         cursor.execute("""UPDATE channel_stats SET joins=joins+1""")
         try:
             if ircutils.isUserHostmask(msg.prefix):
-                name = ircdb.users.getUserName(msg.prefix)
+                name = ircdb.users.getUser(msg.prefix).name
             else:
                 name = msg.prefix
             cursor.execute("""UPDATE user_stats
@@ -198,7 +198,7 @@ class ChannelDB(callbacks.PrivmsgCommandAndRegexp, ChannelDBHandler):
         cursor.execute("""UPDATE channel_stats SET parts=parts+1""")
         try:
             if ircutils.isUserHostmask(msg.prefix):
-                name = ircdb.users.getUserName(msg.prefix)
+                name = ircdb.users.getUser(msg.prefix).name
             else:
                 name = msg.prefix
             cursor.execute("UPDATE user_stats SET parts=parts+1 WHERE name=%s",
@@ -214,7 +214,7 @@ class ChannelDB(callbacks.PrivmsgCommandAndRegexp, ChannelDBHandler):
         cursor.execute("""UPDATE channel_stats SET topics=topics+1""")
         try:
             if ircutils.isUserHostmask(msg.prefix):
-                name = ircdb.users.getUserName(msg.prefix)
+                name = ircdb.users.getUser(msg.prefix).name
             else:
                 name = msg.prefix
             cursor.execute("""UPDATE user_stats
@@ -231,7 +231,7 @@ class ChannelDB(callbacks.PrivmsgCommandAndRegexp, ChannelDBHandler):
         cursor.execute("""UPDATE channel_stats SET modes=modes+1""")
         try:
             if ircutils.isUserHostmask(msg.prefix):
-                name = ircdb.users.getUserName(msg.prefix)
+                name = ircdb.users.getUser(msg.prefix).name
             else:
                 name = msg.prefix
             cursor.execute("""UPDATE user_stats
@@ -248,7 +248,7 @@ class ChannelDB(callbacks.PrivmsgCommandAndRegexp, ChannelDBHandler):
         cursor.execute("""UPDATE channel_stats SET kicks=kicks+1""")
         try:
             if ircutils.isUserHostmask(msg.prefix):
-                name = ircdb.users.getUserName(msg.prefix)
+                name = ircdb.users.getUser(msg.prefix).name
             else:
                 name = msg.prefix
             cursor.execute("""UPDATE user_stats
@@ -258,7 +258,7 @@ class ChannelDB(callbacks.PrivmsgCommandAndRegexp, ChannelDBHandler):
             pass
         try:
             kicked = msg.args[1]
-            name = ircdb.users.getUserName(irc.state.nickToHostmask(kicked))
+            name = ircdb.users.getUser(irc.state.nickToHostmask(kicked)).name
             cursor.execute("""UPDATE user_stats
                               SET kicked=kicked+1
                               WHERE name=%s""", name)
@@ -278,7 +278,7 @@ class ChannelDB(callbacks.PrivmsgCommandAndRegexp, ChannelDBHandler):
         if not ircdb.users.hasUser(name):
             try:
                 hostmask = irc.state.nickToHostmask(name)
-                name = ircdb.users.getUserName(hostmask)
+                name = ircdb.users.getUser(hostmask).name
             except KeyError:
                 irc.error(msg, conf.replyNoUser)
                 return
@@ -369,7 +369,7 @@ class ChannelDB(callbacks.PrivmsgCommandAndRegexp, ChannelDBHandler):
         if not ircdb.users.hasUser(name):
             hostmask = irc.state.nickToHostmask(name)
             try:
-                name = ircdb.users.getUserName(hostmask)
+                name = ircdb.users.getUser(hostmask).name
             except KeyError:
                 irc.error(msg, conf.replyNoUser)
                 return
diff --git a/plugins/Factoids.py b/plugins/Factoids.py
index 7748d278c..cadfa07c9 100644
--- a/plugins/Factoids.py
+++ b/plugins/Factoids.py
@@ -144,7 +144,7 @@ class Factoids(ChannelDBHandler, callbacks.Privmsg):
                 irc.error(msg, conf.replyNoCapability % capability)
                 return
             if ircdb.users.hasUser(msg.prefix):
-                name = ircdb.users.getUserName(msg.prefix)
+                name = ircdb.users.getUser(msg.prefix).name
             else:
                 name = msg.nick
             cursor.execute("""INSERT INTO factoids VALUES
@@ -364,6 +364,7 @@ class Factoids(ChannelDBHandler, callbacks.Privmsg):
                                utils.nItems(cursor.rowcount, 'key'))
             else:
                 irc.reply(msg, s)
+
         
 Class = Factoids
 # vim:set shiftwidth=4 tabstop=8 expandtab textwidth=78:
diff --git a/plugins/FunDB.py b/plugins/FunDB.py
index 1ecb439e5..3e2b92f83 100755
--- a/plugins/FunDB.py
+++ b/plugins/FunDB.py
@@ -262,7 +262,7 @@ class FunDB(callbacks.Privmsg):
         (table, s) = privmsgs.getArgs(args, needed=2)
         table = table.lower()
         try:
-            name = ircdb.users.getUserName(msg.prefix)
+            name = ircdb.users.getUser(msg.prefix).name
         except KeyError:
             irc.error(msg, conf.replyNotRegistered)
             return
@@ -295,7 +295,7 @@ class FunDB(callbacks.Privmsg):
         (table, id) = privmsgs.getArgs(args, needed=2)
         table = table.lower()
         try:
-            ircdb.users.getUserName(msg.prefix)
+            ircdb.users.getUser(msg.prefix).name
         except KeyError:
             irc.error(msg, conf.replyNotRegistered)
             return
@@ -464,7 +464,7 @@ class FunDB(callbacks.Privmsg):
                 irc.queueMsg(ircmsgs.action(channel, '%s for %s (#%s)' %\
                     (praise, reason, id)))
             else:
-                irc.queueMsg(ircmsgs.action(channel, '%s (#%s)' % (praise, id)))
+                irc.queueMsg(ircmsgs.action(channel, '%s (#%s)' %(praise, id)))
         raise callbacks.CannotNest
 
     def addword(self, irc, msg, args):
diff --git a/plugins/Topic.py b/plugins/Topic.py
index 73d488a9b..b2f69cc95 100644
--- a/plugins/Topic.py
+++ b/plugins/Topic.py
@@ -84,7 +84,7 @@ class Topic(callbacks.Privmsg):
                 return
             currentTopic = irc.state.getTopic(channel)
             try:
-                name = ircdb.users.getUserName(msg.prefix)
+                name = ircdb.users.getUser(msg.prefix).name
             except KeyError:
                 name = msg.nick
             formattedTopic = self.topicFormatter % (topic, name)
@@ -166,7 +166,7 @@ class Topic(callbacks.Privmsg):
         else:
             (topic, name) = match.groups()
         try:
-            senderName = ircdb.users.getUserName(msg.prefix)
+            senderName = ircdb.users.getUser(msg.prefix).name
         except KeyError:
             irc.error(msg, conf.replyNoUser)
             return
@@ -208,7 +208,7 @@ class Topic(callbacks.Privmsg):
             else:
                 (topic, name) = match.groups()
             try:
-                username = ircdb.users.getUserName(msg.prefix)
+                username = ircdb.users.getUser(msg.prefix).name
             except KeyError:
                 username = msg.nick
             if name and name != username and \
diff --git a/scripts/setup.py b/scripts/setup.py
index 2e0c28356..676ecdef5 100644
--- a/scripts/setup.py
+++ b/scripts/setup.py
@@ -130,8 +130,7 @@ if __name__ == '__main__':
         filenames.extend(os.listdir(dir))
     plugins = []
     for filename in filenames:
-        if filename.endswith('.py') and \
-           filename.lower() != filename:
+        if filename.endswith('.py') and filename[0].isupper():
             plugins.append(os.path.splitext(filename)[0])
         plugins.sort()
     if yn('Would you like to see a list of the available modules?') == 'y':
@@ -201,12 +200,13 @@ if __name__ == '__main__':
     if yn('Would you like to add an owner user?') == 'y':
         owner = something('What should the owner\'s username be?')
         password = something('What should the owner\'s password be?')
-        user = ircdb.IrcUser()
+        (id, user) = ircdb.users.newUser()
         user.setPassword(password)
+        user.names.add(owner)
         user.addCapability('owner')
         while yn('Would you like to add a hostmask for the owner?') == 'y':
             user.addHostmask(something('What hostmask?'))
-        ircdb.users.setUser(owner, user)
+        ircdb.users.setUser(id, user)
 
     ###
     # Configuration variables in conf.py.
diff --git a/src/AdminCommands.py b/src/AdminCommands.py
index db9e229b0..181d107e0 100755
--- a/src/AdminCommands.py
+++ b/src/AdminCommands.py
@@ -136,9 +136,10 @@ class AdminCommands(privmsgs.CapabilityCheckingPrivmsg):
         if ircdb.checkCapability(msg.prefix, capability) or \
            '!' in capability:
             try:
-                u = ircdb.users.getUser(name)
-                u.addCapability(capability)
-                ircdb.users.setUser(name, u)
+                id = ircdb.users.getUserId(name)
+                user = ircdb.users.getUser(id)
+                user.addCapability(capability)
+                ircdb.users.setUser(id, user)
                 irc.reply(msg, conf.replySuccess)
             except KeyError:
                 irc.error(msg, conf.replyNoUser)
@@ -156,9 +157,10 @@ class AdminCommands(privmsgs.CapabilityCheckingPrivmsg):
         if ircdb.checkCapability(msg.prefix, capability) or \
            '!' in capability:
             try:
-                u = ircdb.users.getUser(name)
-                u.addCapability(capability)
-                ircdb.users.setUser(name, u)
+                id = ircdb.users.getUserId(name)
+                user = ircdb.users.getUser(id)
+                user.addCapability(capability)
+                ircdb.users.setUser(id, user)
                 irc.reply(msg, conf.replySuccess)
             except KeyError:
                 irc.error(msg, conf.replyNoUser)
diff --git a/src/ChannelCommands.py b/src/ChannelCommands.py
index 27a33d2aa..64ca9d81d 100755
--- a/src/ChannelCommands.py
+++ b/src/ChannelCommands.py
@@ -256,9 +256,10 @@ class ChannelCommands(callbacks.Privmsg):
         capability = ircdb.makeChannelCapability(channel, capability)
         if ircdb.checkCapability(msg.prefix, neededcapability):
             try:
-                u = ircdb.users.getUser(name)
-                u.addCapability(capability)
-                ircdb.users.setUser(name, u)
+                id = ircdb.users.getUserId(name)
+                user = ircdb.users.getUser(id)
+                user.addCapability(capability)
+                ircdb.users.setUser(id, user)
                 irc.reply(msg, conf.replySuccess)
             except KeyError:
                 irc.error(msg, conf.replyNoUser)
@@ -280,9 +281,10 @@ class ChannelCommands(callbacks.Privmsg):
         capability = ircdb.makeChannelCapability(channel, capability)
         if ircdb.checkCapability(msg.prefix, neededcapability):
             try:
-                u = ircdb.users.getUser(name)
-                u.removeCapability(capability)
-                ircdb.users.setUser(name, u)
+                id = ircdb.users.getUser(name)
+                user = ircdb.users.getUser(id)
+                user.removeCapability(capability)
+                ircdb.users.setUser(id, user)
                 irc.reply(msg, conf.replySuccess)
             except KeyError:
                 irc.error(msg, conf.replyNoUser)
diff --git a/src/UserCommands.py b/src/UserCommands.py
index 8ad90128a..a32e3a202 100755
--- a/src/UserCommands.py
+++ b/src/UserCommands.py
@@ -36,6 +36,7 @@ Provides commands useful to users in general. This plugin is loaded by default.
 import string
 
 import conf
+import utils
 import ircdb
 import ircutils
 import privmsgs
@@ -61,16 +62,20 @@ class UserCommands(callbacks.Privmsg):
         if ircutils.isChannel(msg.args[0]):
             irc.error(msg, conf.replyRequiresPrivacy)
             return
-        if ircdb.users.hasUser(name):
-            irc.error(msg, 'That name is already registered.')
+        try:
+            ircdb.users.getUserId(name)
+            irc.error(msg, 'That name is alrady assigned to someone.')
             return
+        except KeyError:
+            pass
         if ircutils.isUserHostmask(name):
             irc.error(msg, 'Hostmasks aren\'t valid usernames.')
             return
-        user = ircdb.IrcUser()
+        (id, user) = ircdb.users.newUser()
+        user.name = name
         user.setPassword(password)
         user.addHostmask(msg.prefix)
-        ircdb.users.setUser(name, user)
+        ircdb.users.setUser(id, user)
         irc.reply(msg, conf.replySuccess)
 
     def addhostmask(self, irc, msg, args):
@@ -92,20 +97,20 @@ class UserCommands(callbacks.Privmsg):
             irc.error(msg, s)
             return
         try:
-            user = ircdb.users.getUser(name)
+            id = ircdb.users.getUserId(name)
+            user = ircdb.users.getUser(id)
         except KeyError:
             irc.error(msg, conf.replyNoUser)
             return
         try:
-            name = ircdb.users.getUserName(hostmask)
-            s = 'That hostmask is already registered to %s.' % name
-            irc.error(msg, s)
+            _ = ircdb.users.getUserId(hostmask)
+            irc.error(msg, 'That hostmask is already registered.')
             return
         except KeyError:
             pass
         if user.checkHostmask(msg.prefix) or user.checkPassword(password):
             user.addHostmask(hostmask)
-            ircdb.users.setUser(name, user)
+            ircdb.users.setUser(id, user)
             irc.reply(msg, conf.replySuccess)
         else:
             irc.error(msg, conf.replyIncorrectAuth)
@@ -122,13 +127,14 @@ class UserCommands(callbacks.Privmsg):
         if not self._checkNotChannel(irc, msg, password):
             return
         try:
-            user = ircdb.users.getUser(name)
+            id = ircdb.users.getUserId(name)
+            user = ircdb.users.getUser(id)
         except KeyError:
             irc.error(msg, conf.replyNoUser)
             return
         if user.checkHostmask(msg.prefix) or user.checkPassword(password):
             user.removeHostmask(hostmask)
-            ircdb.users.setUser(name, user)
+            ircdb.users.setUser(id, user)
             irc.reply(msg, conf.replySuccess)
         else:
             irc.error(msg, conf.replyIncorrectAuth)
@@ -144,13 +150,14 @@ class UserCommands(callbacks.Privmsg):
         if not self._checkNotChannel(irc, msg, oldpassword+newpassword):
             return
         try:
-            user = ircdb.users.getUser(name)
+            id = ircdb.users.getUserId(name)
+            user = ircdb.users.getUser(id)
         except KeyError:
             irc.error(msg, conf.replyNoUser)
             return
         if user.checkPassword(oldpassword):
             user.setPassword(newpassword)
-            ircdb.users.setUser(name, user)
+            ircdb.users.setUser(id, user)
             irc.reply(msg, conf.replySuccess)
         else:
             irc.error(msg, conf.replyIncorrectAuth)
@@ -169,8 +176,8 @@ class UserCommands(callbacks.Privmsg):
                 irc.error(msg, conf.replyNoUser)
                 return
         try:
-            name = ircdb.users.getUserName(hostmask)
-            irc.reply(msg, name)
+            user = ircdb.users.getUser(hostmask)
+            irc.reply(msg, user.name)
         except KeyError:
             irc.error(msg, conf.replyNoUser)
 
@@ -197,11 +204,7 @@ class UserCommands(callbacks.Privmsg):
         isn't specified, returns the hostmasks of the user calling the command.
         """
         if not args:
-            try:
-                name = ircdb.users.getUserName(msg.prefix)
-            except KeyError:
-                irc.error(msg, conf.replyNoUser)
-                return
+            name = msg.prefix
         else:
             name = privmsgs.getArgs(args)
         try:
@@ -219,13 +222,14 @@ class UserCommands(callbacks.Privmsg):
         if not self._checkNotChannel(irc, msg):
             return
         try:
-            u = ircdb.users.getUser(name)
+            id = ircdb.users.getUserId(name)
+            user = ircdb.users.getUser(id)
         except KeyError:
             irc.error(msg, conf.replyNoUser)
             return
-        if u.checkPassword(password):
-            u.setAuth(msg.prefix)
-            ircdb.users.setUser(name, u)
+        if user.checkPassword(password):
+            user.setAuth(msg.prefix)
+            ircdb.users.setUser(id, user)
             irc.reply(msg, conf.replySuccess)
         else:
             irc.error(msg, conf.replyIncorrectAuth)
@@ -236,13 +240,13 @@ class UserCommands(callbacks.Privmsg):
         Un-identifies the user.
         """
         try:
-            u = ircdb.users.getUser(msg.prefix)
-            name = ircdb.users.getUserName(msg.prefix)
+            id = ircdb.users.getUserId(msg.prefix)
+            user = ircdb.users.getUser(id)
         except KeyError:
             irc.error(msg, conf.replyNoUser)
             return
-        u.unsetAuth()
-        ircdb.users.setUser(name, u)
+        user.unsetAuth()
+        ircdb.users.setUser(id, user)
         irc.reply(msg, conf.replySuccess)
 
     def whoami(self, irc, msg, args):
@@ -251,8 +255,8 @@ class UserCommands(callbacks.Privmsg):
         Returns the name of the user calling the command.
         """
         try:
-            name = ircdb.users.getUserName(msg.prefix)
-            irc.reply(msg, name)
+            user = ircdb.users.getUser(msg.prefix)
+            irc.reply(msg, user.name)
         except KeyError:
             irc.error(msg, conf.replyNotRegistered)
 
diff --git a/src/asyncoreDrivers.py b/src/asyncoreDrivers.py
index 2c2fa66f2..28601eedd 100644
--- a/src/asyncoreDrivers.py
+++ b/src/asyncoreDrivers.py
@@ -182,7 +182,8 @@ Name: """ % (world.version, sys.version.translate(string.ascii, '\r\n'))
             try:
                 name = self.buffer
                 self.buffer = ''
-                self.u = ircdb.users.getUser(name)
+                id = ircdb.users.getUserId(name)
+                self.u = ircdb.users.getUser(id)
                 self.prompt = 'Password: '
             except KeyError:
                 self.push('Unknown user.\n')
diff --git a/src/ircdb.py b/src/ircdb.py
index 544078ec8..4e4b9aba0 100644
--- a/src/ircdb.py
+++ b/src/ircdb.py
@@ -34,11 +34,11 @@ from fix import *
 import os
 import sets
 import time
-import atexit
 import string
 
 import conf
 import debug
+import utils
 import world
 import ircutils
 
@@ -158,9 +158,10 @@ class UserCapabilitySet(CapabilitySet):
 class IrcUser(object):
     """This class holds the capabilities and authentications for a user.
     """
-    def __init__(self, ignore=False, password='', auth=None,
+    def __init__(self, ignore=False, password='', name='',
                  capabilities=(), hostmasks=None):
-        self.auth = auth # The (time, hostmask) a user authenticated under.
+        self.auth = None # The (time, hostmask) a user authenticated under
+        self.name = name # The name of the user.
         self.ignore = ignore # A boolean deciding if the person is ignored.
         self.password = password # password (plaintext? hashed?)
         self.capabilities = UserCapabilitySet()
@@ -172,10 +173,10 @@ class IrcUser(object):
             self.hostmasks = hostmasks
 
     def __repr__(self):
-        return '%s(ignore=%s, auth=%r, password=%r, '\
+        return '%s(ignore=%s, password=%r, name=%r, '\
                'capabilities=%r, hostmasks=%r)\n' %\
-               (self.__class__.__name__, self.ignore, self.auth,
-                self.password, self.capabilities, self.hostmasks)
+               (self.__class__.__name__, self.ignore, self.password,
+                self.name, self.capabilities, self.hostmasks)
 
     def addCapability(self, capability):
         self.capabilities.add(capability)
@@ -315,103 +316,139 @@ class IrcChannel(object):
                 return True
         return False
 
-
-class UsersDictionary(object):
+class UsersDB(object):
     def __init__(self, filename):
         self.filename = filename
-        fd = file(filename, 'r')
-        s = fd.read()
-        fd.close()
-        Set = sets.Set
-        ignore(Set) # Make PyChecker happy.
-        self.dict = eval(normalize(s))
-        self.cache = {} # hostmasks to nicks.
-        self.revcache = ircutils.IrcDict() # nicks to hostmasks.
-
-    def resetCache(self, s):
-        if s in self.cache:
-            # it's a hostmask.
-            name = self.cache[s]
-            del self.cache[s]
+        if os.path.exists(filename):
+            fd = file(filename, 'r')
+            s = fd.read()
+            fd.close()
+            IrcSet = ircutils.IrcSet
+            (self.nextId, self.users) = eval(normalize(s))
         else:
-            # it's already a name.
-            name = s
-        # name should always be in self.revcache, this should never KeyError.
-        if name in self.revcache:
-            for hostmask in self.revcache[name]:
-                del self.cache[hostmask]
-            del self.revcache[name]
-
-    def setCache(self, hostmask, name):
-        self.cache[hostmask] = name
-        self.revcache.setdefault(name, []).append(hostmask)
-
-    def getUser(self, s):
-        if ircutils.isUserHostmask(s):
-            name = self.getUserName(s)
-        else:
-            name = s
-        return self.dict[name]
-
-    def setUser(self, s, u):
-        # First, invalidate the cache for this user.
-        self.resetCache(s)
-        if ircutils.isUserHostmask(s):
-            name = self.getUserName(s)
-        else:
-            name = s
-        for hostmask in u.hostmasks:
-            try:
-                username = self.getUserName(hostmask)
-                if username != name:
-                    raise ValueError, 'User has hostmasks already matching ' \
-                                      'another user\'s hostmasks.'
-            except KeyError:
-                pass
-        self.dict[name] = u
-
-    def hasUser(self, s):
-        return (s in self.dict)
-
-    def delUser(self, s):
-        if ircutils.isUserHostmask(s):
-            name = self.getUserName(s)
-        else:
-            name = s
-        self.resetCache(name)
-        try:
-            del self.dict[name]
-        except KeyError:
-            pass
-
-    def getUserName(self, s):
-        assert ircutils.isUserHostmask(s), 'string must be a hostmask'
-        if s in self.cache:
-            return self.cache[s]
-        else:
-            for (name, user) in self.dict.iteritems():
-                if user.checkHostmask(s):
-                    self.cache[s] = name
-                    self.revcache.setdefault(name,[]).append(s)
-                    return name
-            raise KeyError, s
-
-    def flush(self):
-        fd = file(self.filename, 'w')
-        fd.write(repr(self.dict))
-        fd.close()
+            self.nextId = 1
+            self.users = [IrcUser(capabilities=['owner'],
+                                  password=utils.mktemp())]
+        self._nameCache = {}
+        self._hostmaskCache = {}
 
     def reload(self):
         self.__init__(self.filename)
 
+    def flush(self):
+        fd = file(self.filename, 'w')
+        fd.write(repr((self.nextId, self.users)))
+        fd.close()
+
+    def getUserId(self, s):
+        if ircutils.isUserHostmask(s):
+            try:
+                return self._hostmaskCache[s]
+            except KeyError:
+                ids = []
+                for (id, user) in enumerate(self.users):
+                    if user is None:
+                        continue
+                    if user.checkHostmask(s):
+                        ids.append(id)
+                if len(ids) == 1:
+                    id = ids[0]
+                    self._hostmaskCache[s] = id
+                    self._hostmaskCache.setdefault(id, sets.Set()).add(s)
+                    return id
+                elif len(ids) == 0:
+                    raise KeyError, s
+                else:
+                    raise ValueError, 'Ids %r matched.' % ids
+        else: # Not a hostmask, must be a name.
+            try:
+                return self._nameCache[s]
+            except KeyError:
+                for (id, user) in enumerate(self.users):
+                    if user is None:
+                        continue
+                    if s == user.name:
+                        self._nameCache[s] = id
+                        self._nameCache.setdefault(id, sets.Set()).add(s)
+                        return id
+                else:
+                    raise KeyError, s
+
+    def getUser(self, id):
+        if not isinstance(id, int):
+            # Must be a string.  Get the UserId first.
+            id = self.getUserId(id)
+        try:
+            ret = self.users[id]
+            if ret is None:
+                raise KeyError, id
+            return ret
+        except IndexError:
+            raise KeyError, id
+
+    def hasUser(self, id):
+        try:
+            self.getUser(id)
+            return True
+        except KeyError:
+            return False
+
+    def setUser(self, id, user):
+        assert isinstance(id, int), 'setUser takes an integer userId.'
+        if not 0 <= id < len(self.users) or self.users[id] is None:
+            raise KeyError, id
+        try:
+            if self.getUserId(user.name) != id:
+                raise ValueError, \
+                      '%s is already registered to someone else.' % user.name
+        except KeyError:
+            pass
+        for hostmask in user.hostmasks:
+            try:
+                if self.getUserId(hostmask) != id:
+                    raise ValueError, \
+                          '%s is already registered to someone else.'% hostmask
+            except KeyError:
+                continue
+        if id in self._nameCache:
+            for name in self._nameCache[id]:
+                del self._nameCache[name]
+            del self._nameCache[id]
+        if id in self._hostmaskCache:
+            for hostmask in self._hostmaskCache[id]:
+                del self._hostmaskCache[hostmask]
+            del self._hostmaskCache[id]
+        ### FIXME: what if the new hostmasks overlap with another hostmask?
+        self.users[id] = user
+
+    def delUser(self, id):
+        if not 0 <= id < len(self.users) or self.users[id] is None:
+            raise KeyError, id
+        self.users[id] = None
+        for name in self._nameCache.get(id, []):
+            del self._nameCache[name]
+        for hostmask in self._hostmaskCache.get(id, []):
+            del self._hostmaskCache[hostmask]
+
+    def newUser(self):
+        user = IrcUser()
+        id = self.nextId
+        self.nextId += 1
+        self.users.append(user)
+        return (id, user)
+
+
 class ChannelsDictionary(object):
     def __init__(self, filename):
         self.filename = filename
-        fd = file(filename, 'r')
-        s = fd.read()
-        fd.close()
-        Set = sets.Set
-        self.dict = eval(normalize(s))
+        if os.path.exists(filename):
+            fd = file(filename, 'r')
+            s = fd.read()
+            fd.close()
+            Set = sets.Set
+            self.dict = eval(normalize(s))
+        else:
+            self.dict = {}
 
     def getChannel(self, channel):
         channel = channel.lower()
@@ -438,26 +475,9 @@ class ChannelsDictionary(object):
 ###
 # Later, I might add some special handling for botnet.
 ###
-if not os.path.exists(conf.userfile):
-    fd = open(conf.userfile, 'w')
-    fd.write('{}')
-    fd.close()
-users = UsersDictionary(conf.userfile)
-
-if not os.path.exists(conf.channelfile):
-    fd = file(conf.channelfile, 'w')
-    fd.write('{}')
-    fd.close()
+users = UsersDB(conf.userfile)
 channels = ChannelsDictionary(conf.channelfile)
 
-def flushUsers():
-    for (name, u) in users.dict.iteritems():
-        u.unsetAuth()
-    users.flush()
-
-atexit.register(flushUsers)
-atexit.register(channels.flush)
-
 world.flushers.append(users.flush)
 world.flushers.append(channels.flush)
 
@@ -473,7 +493,8 @@ def checkIgnored(hostmask, recipient='', users=users, channels=channels):
         if ircutils.hostmaskPatternEqual(ignore, hostmask):
             return True
     try:
-        user = users.getUser(hostmask)
+        id = users.getUserId(hostmask)
+        user = users.getUser(id)
     except KeyError:
         # If there's no user...
         if ircutils.isChannel(recipient):
@@ -507,7 +528,8 @@ def checkCapability(hostmask, capability, users=users, channels=channels):
         #debug.printf('world.startup is active.')
         return _x(capability, True)
     try:
-        u = users.getUser(hostmask)
+        id = users.getUserId(hostmask)
+        u = users.getUser(id)
     except KeyError:
         #debug.printf('user could not be found.')
         if isChannelCapability(capability):
@@ -582,13 +604,5 @@ def checkCapabilities(hostmask, capabilities, requireAll=False):
     else:
         return False
 
-def getUser(irc, s):
-    if ircutils.isUserHostmask(s):
-        return users.getUserName(s)
-    else:
-        if users.hasUser(s):
-            return s
-        else:
-            return users.getUserName(irc.state.nickToHostmask(s))
 
 # vim:set shiftwidth=4 tabstop=8 expandtab textwidth=78:
diff --git a/src/irclib.py b/src/irclib.py
index f40249e81..c70ea171f 100644
--- a/src/irclib.py
+++ b/src/irclib.py
@@ -438,8 +438,10 @@ class Irc(object):
                 # it to abuse our 'owner' power we give to ourselves.  Ergo, on
                 # outgoing messages that change our nick, we pre-emptively
                 # delete the 'owner' user we setup for ourselves.
-                if ircdb.users.hasUser(self.nick):
-                    ircdb.users.delUser(self.nick)
+                user = ircdb.users.getUser(0)
+                user.unsetAuth()
+                user.hostmasks = []
+                ircdb.users.setUser(0, user)
             return msg
         else:
             return None
@@ -455,10 +457,10 @@ class Irc(object):
                                  args=msg.args)
         # First, make sure self.nick is always consistent with the server.
         if msg.command == 'NICK' and msg.nick == self.nick:
-            if ircdb.users.hasUser(self.nick):
-                ircdb.users.delUser(self.nick)
-            if ircdb.users.hasUser(self.prefix):
-                ircdb.users.delUser(self.prefix)
+            user = ircdb.users.getUser(0)
+            user.unsetAuth()
+            user.hostmasks = []
+            ircdb.users.setUser(0, user)
             self.nick = msg.args[0]
             (nick, user, domain) = ircutils.splitHostmask(msg.prefix)
             self.prefix = '%s!%s@%s' % (self.nick, user, domain)
@@ -472,17 +474,12 @@ class Irc(object):
             self.sendMsg(ircmsgs.nick(self._nickmods.pop(0) % self.nick))
         if msg.nick == self.nick:
             self.prefix = msg.prefix
-            if ircdb.users.hasUser(self.nick):
-                u = ircdb.users.getUser(self.nick)
-                if not u.hasHostmask(msg.prefix):
-                    u.addHostmask(msg.prefix)
-                    ircdb.users.setUser(self.nick, u)
-            else:
-                u = ircdb.IrcUser(capabilities=['owner'],
-                                  password=utils.mktemp(),
-                                  hostmasks=[msg.prefix])
-                ircdb.users.setUser(self.nick, u)
-                atexit.register(lambda: catch(ircdb.users.delUser(self.nick)))
+            user = ircdb.users.getUser(0)
+            user.hostmasks = []
+            user.name = self.nick
+            user.addHostmask(msg.prefix)
+            user.setPassword(utils.mktemp())
+            ircdb.users.setUser(0, user)
         if msg.command == 'ERROR':
             if msg.args[0].startswith('Closing Link'):
                 if hasattr(self.driver, 'scheduleReconnect'):
diff --git a/src/twistedDrivers.py b/src/twistedDrivers.py
index acaca3f6b..a9d76e069 100644
--- a/src/twistedDrivers.py
+++ b/src/twistedDrivers.py
@@ -103,7 +103,8 @@ class MyShell(Shell):
         debug.printf(repr(username))
         debug.printf(repr(password))
         try:
-            u = ircdb.users.getUser(username)
+            id = ircdb.users.getUserId(username)
+            u = ircdb.users.getUser(id)
             debug.printf(u)
             if u.checkPassword(password) and u.checkCapability('owner'):
                 debug.printf('returning True')
diff --git a/test/test_ircdb.py b/test/test_ircdb.py
index bbd69a7e7..c31e36f1f 100644
--- a/test/test_ircdb.py
+++ b/test/test_ircdb.py
@@ -255,34 +255,32 @@ class IrcChannelTestCase(unittest.TestCase):
         c.removeBan(banmask)
         self.failIf(c.checkIgnored(prefix))
 
-class UsersDictionaryTestCase(unittest.TestCase):
-    filename = 'UsersDictionaryTestCase.conf'
+class UsersDBTestCase(unittest.TestCase):
+    filename = 'UsersDBTestCase.conf'
     def setUp(self):
-        fd = file(self.filename, 'w')
-        fd.write('{}\n')
-        fd.close()
-        self.users = ircdb.UsersDictionary(self.filename)
-
-    def tearDown(self):
-        os.remove(self.filename)
+        try:
+            os.remove(self.filename)
+        except:
+            pass
+        self.users = ircdb.UsersDB(self.filename)
 
     def testGetSetDelUser(self):
         self.assertRaises(KeyError, self.users.getUser, 'foo')
         self.assertRaises(KeyError, self.users.getUser, 'foo!bar@baz')
-        u = ircdb.IrcUser()
+        (id, u) = self.users.newUser()
         hostmask = 'foo!bar@baz'
         banmask = ircutils.banmask(hostmask)
         u.addHostmask(banmask)
-        self.users.setUser('foo', u)
+        u.name = 'foo'
+        self.users.setUser(id, u)
         self.assertEqual(self.users.getUser('foo'), u)
         self.assertEqual(self.users.getUser(hostmask), u)
         self.assertEqual(self.users.getUser(banmask), u)
-        # The UsersDictionary shouldn't allow users to be added whose hostmasks
+        # The UsersDB shouldn't allow users to be added whose hostmasks
         # match another user's already in the database.
-        self.assertRaises(ValueError, self.users.setUser, 'bar', u)
-        u.removeHostmask(banmask)
-        u.addHostmask('*!*@*')
-        self.assertRaises(ValueError, self.users.setUser, 'biff', u)
+        (id, u2) = self.users.newUser()
+        u2.addHostmask('*!*@*')
+        self.assertRaises(ValueError, self.users.setUser, id, u2)
 
 
 class CheckCapabilityTestCase(unittest.TestCase):
@@ -304,40 +302,44 @@ class CheckCapabilityTestCase(unittest.TestCase):
     channelanticap = ircdb.IrcChannel()
     channelanticap.addCapability(anticap)
     def setUp(self):
-        fd = file(self.filename, 'w')
-        fd.write('{}\n')
-        fd.close()
-        self.users = ircdb.UsersDictionary(self.filename)
+        try:
+            os.remove(self.filename)
+        except:
+            pass
+        self.users = ircdb.UsersDB(self.filename)
         self.channels = ircdb.ChannelsDictionary(self.filename)
-        owner = ircdb.IrcUser()
+        (id, owner) = self.users.newUser()
+        owner.name = 'owner'
         owner.addCapability('owner')
         owner.addHostmask(self.owner)
-        self.users.setUser('owner', owner)
-        nothing = ircdb.IrcUser()
+        self.users.setUser(id, owner)
+        (id, nothing) = self.users.newUser()
+        nothing.name = 'nothing'
         nothing.addHostmask(self.nothing)
-        self.users.setUser('nothing', nothing)
-        justfoo = ircdb.IrcUser()
+        self.users.setUser(id, nothing)
+        (id, justfoo) = self.users.newUser()
+        justfoo.name = 'justfoo'
         justfoo.addCapability(self.cap)
         justfoo.addHostmask(self.justfoo)
-        self.users.setUser('justfoo', justfoo)
-        antifoo = ircdb.IrcUser()
+        self.users.setUser(id, justfoo)
+        (id, antifoo) = self.users.newUser()
+        antifoo.name = 'antifoo'
         antifoo.addCapability(self.anticap)
         antifoo.addHostmask(self.antifoo)
-        self.users.setUser('antifoo', antifoo)
-        justchanfoo = ircdb.IrcUser()
+        self.users.setUser(id, antifoo)
+        (id, justchanfoo) = self.users.newUser()
+        justchanfoo.name = 'justchanfoo'
         justchanfoo.addCapability(self.chancap)
         justchanfoo.addHostmask(self.justchanfoo)
-        self.users.setUser('justchanfoo', justchanfoo)
-        antichanfoo = ircdb.IrcUser()
+        self.users.setUser(id, justchanfoo)
+        (id, antichanfoo) = self.users.newUser()
+        antichanfoo.name = 'antichanfoo'
         antichanfoo.addCapability(self.antichancap)
         antichanfoo.addHostmask(self.antichanfoo)
-        self.users.setUser('antichanfoo', antichanfoo)
+        self.users.setUser(id, antichanfoo)
         channel = ircdb.IrcChannel()
         self.channels.setChannel(self.channel, channel)
 
-    def tearDown(self):
-        os.remove(self.filename)
-
     def checkCapability(self, hostmask, capability):
         return ircdb.checkCapability(hostmask, capability,
                                      self.users, self.channels)