It is well known that the ATI fglrx driver produces flickering video in combination with compiz/AIGLX. One solution is to switch to kwin while playing DivX files, DVDs etc.; in this case fusion-icon is your friend ;-)
Nevertheless, with the latest driver (fglrx 8.476 aka AMD Catalyst 8.4) I was in for something special: trying to watch a movie with kaffeine on any window manager crashed my X session instantly. I ruefully reverted to fglrx 8.455.
Morale: Always keep a backup of the last remotely stable driver installer.