Two simple tricks. I tried them with the new 12.1 and they work well. I don't know about older versions. Catalyst's performance on GNOME 3 and Adobe Flash was terrible; with these fixes, it is more than alright.
Simply add this to your /etc/profile file to fix GNOME 3:
# Catalyst fix for Gnome-shell
And for Adobe Flash turn your /etc/adobe/mms.cfg file to this:
#Hardware video decoding