Comment 4 for bug 97037

After the Compiz 0.3.6-1ubuntu11 update, I disabled the nvidia driver with restricted-manager and rebooted before disabling Compiz, it just loaded metacity when I logged back in.

Before that update it horribly broke when I tried to log back in, so maybe it's fixed now.

The changelog says:
compiz (1:0.3.6-1ubuntu11) feisty; urgency=low

  * debian/compiz.wrapper:
    - use metacity and not gnome-wm if compiz doesn't work (Ubuntu: #97053)

 -- Sebastien Bacher <email address hidden> Sat, 31 Mar 2007 14:41:02 +0200

which was four days after this was reported so maybe it's fixed for you already.