Comment 32 for bug 528094

It looks like this should be part of the xscreensaver package, so that the lock screen menu item will work. Either that, or the Session Menu should look for xscreensaver vs gnome-screensaver, and enable the appropriate method. I am assuming the DBUS object is created by gnome-screensaver, so the easiest thing to integrate xscreensaver and Gnome would be to change the xscreensaver package, though really it's Gnome's Session Menu that fails here. From my point of view, the Session Menu should look for a way to lock the screen (gnome-screensaver, xscreensaver) and create the appropriate DBUS object. If no screensaver is present, then the screen can't be locked and the menu item shouldn't be available. Doing it right would require changing gnome-screensaver and the Session Menu.