I found it surprisingly difficult to walk in to a Best Buy or the now late Circuit City and find a card that would "just work" in Linux. I refused to buy nvidia because I'd been an nvidia guy for the last many years and I just got tired of the voodoo I had to do to my machine to get the cards to work right.
I did end up getting a radeon and while some features are missing, it does work without much trickery. I'm happy to hear these reference guides will be released so the radeon drivers can be made even better.
I like to think that us Free software people are very vendor loyal, I know I try to be. I look forward to purchasing more ATI/AMD stuff in the future