Probably a stupid problem and not a bug but..
Latest rawhide :
$ rpm -q compiz metacity compiz-0.0.13-0.17.20060817git.fc6 metacity-2.15.34-1.fc6
When I try : System-->Prefs-->More Prefs-->Desktop Effects
It seems to remove all window management, I get all the applications from my eight workspaces on the one screen, I can no longer switch between workspaces (which has been reported before so I understand this issue) and the applications no longer have borders and are unable to be manipulated.
Anybody else seen this or have I a bodgy setup?