Using Fedora 7 with Gnome 2.18.2 and Desktop Effects enabled (Compiz) my system will almost always crash when I shut down from within Gnome.  However, when I turn off desktop effects and use the default (Metacity) I can shut down normally.  This problem also prevents me from logging out or switching window managers during a session (i.e. - using "metacity --replace").  When I go to shut down and it crashes it clears the screen of all windows and icons on the desktop, but my two Gnome panels on the top and bottom of the screen remain (icons cleared however).  After that, the system is completely unresponsive and can only be shut down manually (holding down the power button).