I've been experiencing tearing when trying to watch movies (both VLC and mplayer) and have had issues with Quadrapasel (a.k.a. gnometris). I tried all the solutions I could find in here with no luck. The next thing I tried was to just disable the official ATI drivers (I have an integrated 3200) and use the open source drivers. That fixed both issues.

As with all fixes, this may not work for everyone. But its something to try if your stuck.