I have found a weird behaviour with two rendering engines in fullscreen mode in Oneiric with Catalyst 11.11. When going fullscreen, Ogre3d and Lime applications display some weird chessboard like artifacts. Unigine demos works perfectly. My video card is an XFX HD5770.
I found one major bug with my hd 5670 and 11-12, are you sure you mean 11-11? gl2benchmark test 1 does not render correctly and xbmc-xvba is completely broken with 11-12. hd 4550 does not suffer from this problem. But maybe amd wants that you change the driver for each app you want to run 12 drivers a year, 12 extra bugs...