So far, having menus and other popups pop over the gnome panel was merely an annoyance, but with gnome-shell being a compositor, the override-redirects actually pop _under_ the panel, and that is just broken.

One argument for why we haven't added this so far is that this is WM territory.

Another argument for why we haven't done it yet is that doing it properly and without constant roundtrips requires us to listen for PropertyChange on the root window, and we don't want to wake up every gtk client in the session whenever the user changes the window stacking, etc. This can be worked around by a property notify filtering api in xfixes that ajax started to spec out at some point.

Wether to make this X-specific or not ? Win32 certainly has this information available: http://msdn.microsoft.com/en-us/library/ms921268.aspx

I'll attach a patch that adds a private, roundtrippy implementation of gdk_screen_get_monitor_workarea and uses it throughout gtk.