“#xkcd has had about 250 chatters these days. Large communities suck. This problem is hard to solve, but we’ve come up with a fun attack on it — enforced originality (in a very narrow sense). We’ve put together an auto-moderation system in an experimental channel, #xkcd-signal, and it seems to work well, so we invite you all to take part.”

http://blag.xkcd.com/2008/01/14/robot9000-and-xkcd-signal-attacking-noise-in-chat/