However, I haven't actually been using the opensource drivers that much. Its been try it out -doesn't work, go back to fglrx.
With XAA, things are unbearable, enabling EXA the configuration get more usable. Part of the problem I think is due to my huge resolution for my main monitor (2560x1600) i.e. its using a dual-link connection. Dunno, there must be some bugs there. For one, I cant set a virtual resolution beyond 4060x1600 without getting the ridiculously slow redrawing on the screen - but this means I have overlap on my monitors
As an aside, I know I am not the only one having problems with the open source drivers:
some other threads as well.
P.S. I am just pulling in xf86-video-ati-6.12.0 which hit the portage tree so will see if it helps out.