I've been having problems with my new 2.53 MBP too. I loved the computer at first, but when I started playing games on it, everything went to hell. While I don't have the black screen issues that others are having, I'm getting very subpar game performance on both Bootcamp Windows XP and OSX.
After playing WOW for 20-30 minutes, my frame rate would drop dramatically. Upon starting the game, I would get anywhere from 70-190 fps. About 30 seconds to a minute of running through the game, my fans would kick into full gear (6200+). Then, after a few minutes, my frame rate would dip to almost 20 and below. The game would run perfectly fine for 5 seconds, dip, run fine, dip. It almost looked as if everything were stuttering.
Now, I'm playing the game with all settings on high (except shadow detail), and I just assumed that a $2300+ machine would be able to run a 4-year-old game (granted, they've been sprucing up the graphics gradually) reasonable well. The same issue is true for the Windows XP side of things.
I've been monitoring my temps with iStat, and the CPU hasn't reached more than 176F, and the GPU hasn't reached more than 170F.
I got fed up with the problem (my early 2007 MBP ran the game much cooler and smoother with only slightly decreased settings) and decided to take it into the Apple store. The Genius told me that the computer shouldn't be running that hot (though another Genius was having the same problem with his... Go figure) and sent it in for repair. He said that they would probably replace the heat sink or logic board. Honestly, I'm skeptical that will solve the problem, but we'll wait and see. If it isn't fixed when I get it back, I'll just return it until I get a working machine.
At this point, I'm wondering why I even splurged for the upgraded video card if I'm unable to use it as it was intended. I'm very, very frustrated.