you'd be surprised what these little silvery machines can do ^_^. I play Oblivion on my MBP SR 2.2Ghz, and it runs FANTASTICALLY. I get around 66fps on sewers (the ones at the start of the game, hey im not that good on RPGs!), and outside it kinda drops to around 40-something. Of course, I only have 128mbs of vram, so the grass, and trees and everything else has to be loaded on the fly, so it stutters from time to time (I guess with 256mbs of VRAM that wont be an issue).
If you're going to be running these kinds of games however, i do advise you to get a cooling mat, or some other kind of refrigeration. Remember, MBPs run a bit on the hot side, and a game like Oblivion (which isn't that well coded to begin with), may cause your system to run through its paces.
cheers.