I am using ubuntu 12.10 and today after i updated my software, when the computer restarted, the icons and menu bars on the desktop did not show. The a icons on the desktop itself still showed but nothing else (no launcer buttons, no time, nothing). Im not sure exactly what caused this. I could not find anything anywhere else. I tried the compiz ccsm unity thing but to no avail. It tells me that unity is running. I tried to unity --reset but I just get told that it is deprecated. Im not sure what to do.
The above might be a useful thread on how to reset unity in 12.10.
My apologies; this should probably be a comment not an answer but I don't have comment privileges yet. If someone wants to edit this answer and convert to a comment I'd be delighted.