Comment 3 for bug 875038

From the blog in question here is the solution in a nutshell:

There were issues with the AMD proprietary driver (“fglrx”) for both my 5770 and 5870 graphics. After removing the proprietary AMD driver, some residual issues still persist.

sudo apt-get remove --purge fglrx fglrx_* fglrx-amdcccle* fglrx-dev* xorg-driver-fglrx
sudo apt-get remove --purge xserver-xorg-video-ati xserver-xorg-video-radeon
sudo apt-get install xserver-xorg-video-ati
sudo apt-get install --reinstall libgl1-mesa-glx libgl1-mesa-dri xserver-xorg-core
sudo mv /etc/X11/xorg.conf /etc/X11/xorg.conf.backup