I really think Linux users don't fathom how fast the ATI drivers are compared to Windows. It's easy for people to think Windows still has the credentials for gaming and general graphics apps, over Linux.
My only gripe is compatibility with Wine. Nvidia seems to be the better option for running Windows Games on Wine. I really hope ATI can spend some time with Wine Devs or doing their own investigations on how to improve. Example, many are having trouble with new 'Elder Scrolls - Skyrim' on ATI withd Wine whilst Nvidia people are smooching it through. Everquest is another games where graphics doesn't draw properly.
Another note is ATI really have done work to improve KDE/QT with OpenCL doing desktop drawing. It's so fast now.