Bah! Cut the fanboy crap! I wouln't worry too much about the "eeeeewww" factor of switching to nVidia anymore. At least they cleaned up their act w/ the new 6x00 cards. The 6800 GT's are performing excellently; and in some of the latest benchmarks, even the 6600 GT's (a midrange card) are nearly on par w/ the x800 pro. The bonus w/ the 6800 GT is that you don't have to do any mod to get the 16 pipes, and a lot of ppl are having great success overclocking the GT's to Ultra speeds.
Bottom line: Unlike last generation (9800 vs 5900), you really can't go wrong w/ either a x800 or a 6800 based card. In some cases (most dx9) the x800 will win out, and in some (mainly ogl) the 6800's will have the edge. In either case, the difference isn't that noticable, typically ~2-5 fps average (from what I've seen).