In my current setup in Gnome Control Center I can select background image (as opposed to simple fill) and specify none should be used. This results in gnome putting random parts of previosly displayed windows on the desktop (in fact, the bitmaps do not neccessarily come from the same X session or X server, seems that part of the graphics memory is allocated for bitmap but never painted) . Although this is a cool effect which could not be easily achieved on purpose it is probably not the intended behavior.
XFree86-server-4.1.0-22mdk libgnome-db0-0.2.93-3mdk libgnome-vfs0-1.0.2-2mdk gnome-control-center-plus-1.5.11-3mdk libgdk-pixbuf-gnomecanvas1-0.14.0-1mdk gnome-libs-1.4.1.4-1mdk libgnomeprint15-devel-0.34-1mdk libgnome-db0-devel-0.2.93-3mdk libgnome32-devel-1.4.1.4-5mdk gnome-core-1.4.0.6-12mdk gnome-control-center-1.5.11-4mdk libgnome32-1.4.1.4-1mdk libglade-gnome-db0-0.17-2mdk rep-gtk-gnome-0.15-4mdk libglade-gnome0-0.17-2mdk i740 graphics card
