I think guy above was talking about the proprietary driver. While I have tried to be a fan of AMD/ATI because of their stance on opensource, for a long time AMD proprietary drivers sucked and had all sorts of problems and the open ones were noticeably slower. For a lot of people there wasn't really much choice.
Sounds like things are much better these days.
Because( no offense to the nouveau guys, you do great job, all things considered) but the open source one is in pretty bad shape and that is completely the fault of Nvidia.
Having to extra compile their driver (that does not conform to kernel standards) delivers a subpar experience for Linux users and taints the kernel. If they don't care about Linux users and help develop the open source driver, they I don't see any reason for buying their hardware. I rather spend it on hardware manufacturers that try to support me as a customer.