If you’ve ever been in #xkcd-signal in irc, you know how it used to be spammed quite alot with people agreeing with a statement, where you see a long stream of, “I agree!”, “haha”, “lol”s
Well…the people at xkcd have developed a rather interesting bot. This is their hypothesis:

Once a community grows past a certain point, quality begins to deteriorate. Their example are sororities or IRC channels. Both can grow so big that you loose touch with everybody and it breaks down. You get more random crap than you get actual information. Instead of a strict entry requirements, moderators, peer moderation, or splinter communities, kxcd created a bot that keeps track of the channel log. It analyzes channel logs and does not allow you to say what has already been said. Example: someone in the past said “lol”. You..now, may not type “lol” and have it show in the channel. A better example, would be agreements. Instead of simply typing “I agree”, which is now banned, you must explain yourself. While there may be some disadvantages, the biggest one that pops up instantly is…you’ll run out of things to say! However, this bot has been running for some time now in the xkcd channel, and with 2 million lines of logs, people are still typing away. They expect a channel to continue function roughly normally for a decade…
Check it out: xkcd ROBOT9000
If you want to try it on your own channel, the code is there. It’s a Perl bot, with sql skeleton.