I've written a votebot or two, but never one for slashdot or PerlMonks. In the world of text-only dial-up or telnet BBSes, I've used bots to downvote users automatically for 133t5p33k and for double posting. I think those are reasonable enough criteria for a downvote, and they aren't difficult to detect.

Of course, when you're an admin with unlimited votes, it's easy to get carried away with that. I used to have so much fun sometimes upvoting a person one day only to downvote them the next. Ah... the good old days.

Chris