https://bugs.freedesktop.org/show_bug.cgi?id=35697
--- Comment #14 from Michel Dänzer michel@daenzer.net 2011-03-28 03:00:50 PDT --- (In reply to comment #13)
Actually, I traced it down to compiz being unable to update the screen. Ctrl-Alt-F1 to the console, "killall -9 compiz" and starting another non-GL window manager, the desktop is usable just fine.
That really sounds like bug 35452.