I got the same problem. What happen has that my Ubuntu 10.10 was updating and then the daemon died (maybe because i was running firefox at the same time and there was a firefox update??).

With the daemon killed there was nothing i could do: opening terminal just open a grey background window, could't mount devices saying that they were read-only files, and to shut-down i had to use the shortcut that shows when ctrl-alt-del is hit because the other shortcut only display an empty dialog box.