I'm running a fresh install of stock Ubuntu, with GS added from the gnome3 ppa. There is no option for shutdown/restart in the session menu. I've had a similar problem from a mis-matched Alternate Status extension in the past, but disabling that extension made no difference.
Second, attempting to log out brings up the gray screen with a top bar, but no greeter/login apparatus. This is with gdm. With lightdm, logout works normally, but the problem with the session menu remains.
Anyone else seeing this? I searched launchpad, but didn't find anything.