After upgrading to 12.04 the system starts up normally, and shows me the login screen.
After I log in, unity does not seem to start up and shows me a small XTerm window.
I start unity manually from there by typing into the command. The xterm window stays open and if I close it it takes me back to the login screen. The theme also seems to be totally messed up. Other than that every thing seems to be working...
I have also reinstalled the ubuntu-desktop package several times, does not seem to help