Just installed Ubuntu 12.10 on my Desktop (i5 3570k, Radeon HD 7950 & 8 GB RAM) and after installing some programs, updating, and restarting; the logon screen loads with the menu bar on top and everything.
But as soon as I log in it disappears, leaving me only with my wallpaper.
I can start the Terminal with
(http://www.webupd8.org/2012/10/how-to-reset-compiz-and-unity-in-ubuntu.html) without success.
I can see my apps are running. (That is, my Dropbox still comes with updates every time I synchronize a file.)