Comment 38 for bug 803943

Unloading unity plugin and decorator makes no difference in my case.
64 bit with fglrx (Catalyst 11.10).

With top running in a terminal;

1: Open a browser, type a non-existent address in, such as http://non-existant-garbage.com
Compiz and Xorg cpu usage spikes to about 50% and 40% respectively and will continue to remain there until the browser request is cancelled (or until there is no spinning load icon or mouse pointer change or the windows is minimised)

2: Open software centre and install a program. Compiz and Xorg will spike and remain high until the program has installed and there is no spinning progress icon in the top bar.

Sounds like a polling issue?