I think what AMD is doing is great too. But if you bought something like a HD4870, even after 3years, under Linux, its still utterly useless for what it was intended for.
There simply aren't enough independent driver writers using the docs and developing features that the community actually wants in order to justify buying hardware from AMD on the basis of their open source initiative when they clearly disregard official Linux support (i.e crappy catalyst).
You're better off buying Nvidia, because you'll be getting excellent official Linux support and you'll be supporting a true open source community that has worked hard to reverse engineer complex hardware for no personal gain.
Don't be fooled by AMD's open source contributions. If they were really committed to open source GPU support, they would have open source developers on their payroll like Intel does.
Take it from someone who has bought a lot of ATi graphics cards, the momentary monetary savings, are simply not worth the years of frustration.