When it works fine with open source Intel, open source ATI, open source Nvidia, closed source Nvidia, but not closed source ATI signs point to not being Gnome-shell.
For the games I play ATI proprietary drivers so far have been worse then the open source ones. I think what Bridgeman and others say about spending a lot of time on optimizing specific applications is probably correct. Once you stray outside the set of applications they put a lot of effort on then the proprietary driver falls flat. You start running into bugs and poor performance.
I can live with 80% performance if OSS folks optimize for general case, rather then specific case. That way it works as well for everything.. including stuff they never tested or optimized for.
You are probably right about the gnome-shell issue...it probably is an ati catalyst driver issue. I don't like gnome shell that horribly much in the first place. It's OK, but not better than any other DE at this point, so I don't care, I'll just use others.
Even so, the OSS ati driver doesn't do video accel on my card in any application (last I knew), and I personally have had very poor results with games...especially the humble indie bundle games...where the proprietary drivers have worked fine.
That's not true at all. What may have been said was that performance was considered less important than getting the cards (and newer hardware) to actually work. And that it was unlikely the OSS drivers would get more than 80% or so of the performance of the proprietary drivers, due to lack of manpower and a desire to keep the drivers relatively simple and maintainable. But they do care about getting the drivers to perform at a decent level. It just is taking a while to get them to that point.
There are lots of reasons to grab an NVidia card or even to use fglrx with ATI cards, but you can't just say AMD "doesn't care."
Descent level or not, bottom line, they don't fit for the job. I am AMD fanboy myself, but I do change my opinion of brands, based on performance.
AMD are best so far in OSS performance(i dont take intel seriously here), but it's monopolism really.