Oh happy day! The buildbot.net trac instance just recently got visited by the link spammers. They haven't caused any actual damage yet, just a user account created with advertising in the profile text, but I'm afraid it's only a matter of time before the bots descend upon us and we're smothered by a wave of sentient AIs dedicated to filing mass buildbot bug reports containing nothing but links to offshore casinos and faux designer watches.
I guess I should add some sort of "prove you can read" test to the account-creation page, just barely enough to make the script kiddies work for a living. Something like "what is 1+2?" or "type the word 'please' in here" or something.
Reminds me of a suggestion someone made to me while I was working on petmail: you don't need super-clever CAPTCHA techniques if you can manage to have a whole bunch of different requirements instead, like each user creating their own simple technique. A bot could be written to mass-solve any particular one, but since everybody is creating their own, the bot-writers job is that much harder.
And sometimes, just raising the bar a bit is good enough for now. As the joke goes, I don't have to outrun the lion.. I just have to outrun you :-).