I have the Nvidia go 5600 FX and it works great for me, Granted it lacks when it comes to Directx games but the stability is beyond that of the Radeon.
To sum it up with a few associations.
Nvidia = Stability, Proficiency w/ opengl, geared to animators or graphix pros, difficulty with high fps on DX games or apps.
ATI = Fast DX renders, opengl below nvidia, poor driver support, poor stability, takes modded or six releases of drivers to get to function the way you'd expect, Common porblems with artifacts in textures. Fast FSA & FFAA
It's your choice but if you go ATI either be patient or try to find drivers that better support it than ATI's.
PS Nvidia rumorly will have a 40% increase in overall DX performance when DX9.1 is released since DX was directed at ATI cards when orginally designed. I have no verification but may be something to look at latter.
Hope this helps.
