I have it running right now on a Mac Mini. My PC died over a year ago, and since I had a Mac laptop for school, I couldn't bring myself to spend the $$ for a machine that would only be for games.
Then the intel Macs came out, and I convinced myself that I could get one--I can use it as a Mac to log into the servers at school and get programming done, and as a PC to play the PC games I've been missing.
Performance-wise, bootcamp has run all my windows games no problem. I might have trouble trying some of the newer games because the Mini has an integrated graphics card, but my older games all run well (BG2, MOO, Quake2, Freelancer, IWD, etc.)
There's a
bootcamp discussion forum on Apple's site. People there have reported that with the more powerful Macs that have good video cards, even the new games run well under bootcamp.
If you're thinking of going this route, you might want to wait for the next OSX version to come out. One of it's features will be a built in version of Bootcamp (the one out now is officially a beta product and so there's no tech support).
One of the nicest benefits for me is that I disabled all internet connections on the XP side. If I need to surf the net or download a file, I use the Mac side or my laptop. So I have no need of anti-virus or -spyware programs, and XP doesn't get bogged down. Of course, if you want to play online, you can't go that route.