Comment 3 for bug 94285

I had the same problem until I found that thread: http://forum.ubuntuusers.de/topic/79023/?highlight=gnomesession

ESD is the problem.
I logged into a safe xterm session, started esd manually and then gnome-session.
After I disabled esd everything worked again.

Shortly before I wanted to try pulseaudio, maybe that was the cause.
Stracing gnome-session showed me, that it wanted to make a connection to localhost:16001 and hanged there forever.