Now that there is the possibility that nVidia will NOT be able to wrest the performance crown away from ATI (in upcoming generation) it is only fitting that Apple goes with them and not ATI (in a typical performance limiting choice.)
From my limited understanding I have garnered this: it is not so easy to add lots of parallel programmability and yet make dramatic increases in outright speed (polys, textures, fill rate yadda yadda). Look at Matrox and their Parehalia, it doesn't really provide better performance than a Ti4600 on any of today's games. But, it might perhaps be able to do more interesting things in the future.
Rumor has it that nVidia isn't really 100% stoked about nv30. At one point one of their people might have suggested that they wouldn't meet their own performance expectations because they'd spent too much time on other projects (x-Box, nForce). That's interesting.
ATI now has two cards which are both FAST and eqully programmable, differing only in speed, but also, as is usually an ATI forte, the bottom spec can enter the market at a consumer/OEM friendly price where it will kill anything nVidia currently has in that space.
So, after years of ATI, apple could change only to find itself on the second tier card yet again. HAHAHA!!!
Realistically, both ATI and nVidia should offer admirable performance in the next generation, but I'm really interested to see if ATI has any notebook plans for its 9000 GPU ???
yes yes, I know nVidia has the best outright performance at the moment and that Apple uses their product, but for what seemed like the longest time we pined for nVidia, nVidia, and now that we might get all nVidia, it might have been better to go with ATI.