For example there is no logout button:

If I log in with the guest session, everything seems to be fine (there is a log out button). I tried to remove my whole user directory and create an empty one, but the problem remains.

I am running Gnome Shell 3.4 using the PPAs ppa:gnome3-team/gnome3 and ppa:ricotz/testing as described in this answer. I disabled all shell extensions and restarted the computer, but the problem remains.

Another difference between my user and the guest user I noticed: when I close the last window on the current workspace, the activitiy overview appears. This annoying beheviour seems to be disabled for the guest user.

I'm thinking to switch to Debian. I try to get 12.04 running with Gnome Shell since 2 days now...