I'm and Intel/nVidia guy. I have had bad run ins with ATI and AMD is basically good for mid-grade CPUs. High-end CPUs is Intel's market.
nVidia is also the leader of single GPU design. The GT200 destroys ATI's offerings. It is only when you put it against the GPGPUs that the single GPU falls short.
Nahelam + GT??? = awesome. I can't wait for PCI 2.0 to be taken advantage of. The 5GB/s i/o rate will bring things to the next level.