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Look at their supported products :

GeForce 200 series:
GTX 285 for MAC

GeForce 100 series:
GT 120

GeForce 8 series:
8800 GT

Quadro series:
4000 for Mac

Quadro FX series:
FX 5600, FX 4800 for MAC
 
Look at their supported products :

GeForce 200 series:
GTX 285 for MAC

GeForce 100 series:
GT 120

GeForce 8 series:
8800 GT

Quadro series:
4000 for Mac

Quadro FX series:
FX 5600, FX 4800 for MAC

according to users on netkas, support for GTX 580 and 570s are running out of the box. Just no boot screen.
 
A further look at the future, Mac's becoming more mainstream, more games being released etc.

I'm not going to be upgrading the 2GB in my iMac, but Power PC and mini users? If you want to okay games, that;s the way to go.
 
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