The most important thing in my book is stability. And the proprietary drivers for ATI never delivered that and were focused mostly on performance above all else.
Personally I think that stability matters. And the open source drivers can deliver that. They can, with the help of involved users, fix bugs fater, support hardware longer, and provide a high quality out-of-the-box experience for Linux.. which the proprietary ATI drivers never could.
So ATI/AMD should be hailed and congratulated for what they have done.
Let them worry about the latest and greatest and getting the last 10% of the performance that some folks need... I want decent performing, reliable, stable, and zero effort 3D acceleration; which is what the OSS drivers can deliver.
Don't underestimate the high quality of experience that zero effort can deliver. Seriously. Having things 'just work' is WONDERFUL and makes it much easier for everybody... from the developers to the end users.
When shit 'just works'... Linux is _SLICK_. It's a terrific operating system and surpasses even OS X in many ways in terms of usability. But we can't get there relying on proprietary drivers... they just can't deliver what is required.