[MrGatorade]

Poker stars does have them and are targeted to suspected winholdem bot users. Private and non public bots are also getting the captchas because of the anti-bot technology they have. PokerStars is by far the best site to play on because the bot users actually have to baby sit there bots to not get caught. PokerStars understands there integrity of there games needs to be the formost important part of there business.
FullTilt - Lots of bots and they dont care, ignore there presense.
UltimateBet- Absolutly doesnt care and lets them run rampant and denies bots can play on there site.
WPEX- Bots, Bots, and more bots. Currently investigating site.
Absolute- Same as UB.

You can find more on my site as I am in the process of gathering lots of information and doing a major update and upgrade on exactly how to find the bots yourself. Major poker magazines and media outlets are also about to get involved. =)

-MrGatorade (Crazy Mike)