put some web sense into your bots. In fact, buy WebSense (or one of their competitors) and create some new categories:
1) SEO firms (all they do is keep your AI developers employed)
2) aggregators (why would you ever index another search engine)
3) competitors (why drive business to them...unless they run adwords?)
And stop indexing them. If you don't index them, then you can't be taken to court because you "filter" your search results because there won't actually be any pages to search to generate results.
This isn't evil, not really, well, it is actually. But not as evil as sending a guy with sandpaper and rubbing alcohol to make sure they understand the message "Don't ever do that again!" Also evil would be having competitions for 'the least desired category of the month' and then dropping them from your indexing bot for 90 days....that would be evil.
Vote me up, that's ok. Vote me down, that's ok too, but I'd ask you to explain your solution to the problem.