In recent rawhide, when the top panel is set to autohide, the desktop icons follow it as it hides and unhides. This is with metacity. I'm told that with compiz, windows are jumping up and down too. http://bugzilla.gnome.org/show_bug.cgi?id=547828
Also see http://bugzilla.gnome.org/show_bug.cgi?id=529031 for the change responsible for this
Fixed in 2.23.92