On 5th May 2010, there was an update to “libgnome-window-settings1” and related packages (”capplets-data” & “gnome-control-center”). This caused terrible compiz performance (CPU often spiking to 80%). Workaround is to downgrade to the previous version, I also recommend locking the version via Synaptic/Aptitude for the time being.
Workaround - downgrading the package:
aptitude install libgnome-window-settings1=1:2.30.0-0ubuntu4
Launchpad bug: https://bugs.launchpad.net/bugs/576604