I'd noticed recently that my CPU usage had crept up on my ACER laptop with an ATI graphics chip and was slowing down simple things like scrolling. I switched off my folding@home client straight away, and then delved deeper.
I tried the usual fix-all of moving my .gconf path so it would be recreated next time I started the Gnome GUI but this made no difference.
I discovered an option however on the Xorg file xorg.conf which controls the graphical setup. Simply adding the following 2 lines to my xorg.conf file and then restarting gdm and all was back to normal. I love it when a problem like this can be fixed by typing 2 lines into vi ;-)
Identifier "Configured Video Device"
Option "AccelMethod" "XAA"
Sweet potatoes, as they say.