Finally!!! An almost stable (96%) catalyst version 12.3 available for GNOME 3...

no more lagging during the transition between working and activity mode

windows 7 aero effect working perfectly under vmware

catalyst version 12.3

virtual desktop movement is quite smooth

Update (13/04/2012)
Solved laggs/slow windows movement in GNOME3 by adding this line

export CLUTTER_VBLANK=none

into ~/.profile or into /etc/profile file. Restart X server or reboot system.

ref: ATI Catalyst - ArchWiki.