i have used both Nvidia and ATi......GF4MX----------->GF3 TI200--------->Radeon 9500pro....
certainly i have had a few niggles but nothing major like, games not running properly or at all, no incompatibilities with the rest of my system either.
though nvidias 2d and texture settings seem better....i use the omega drivers with my ATI and in a few games when i have performance mode enabled on my ATI textures in some games have become fuzzy and blurred!! not a problem tho..jus slide the bar to balanced and all was fine
colours had a bit more energy on Nv tho