After Upgrade from 11.10 to 12.04, the login process of Gnome 3 is extremely slow (It takes in the order of 60 seconds when it was in the order of a few seconds before the upgrade (Harddisk is a SSD!)).
Running "top" in a VT shows that gnome-shell is producing about 90% CPU load while dbus-daemon is taking roughly 10%. The moment when CPU-load of gnome-shell drops to normal levels (around 2-3%) corresponds to the time the login process is terminated and the desktop is displayed.
De-activating the four gnome-shell extensions (Alternative Status Menu, Quit Button, Remove Accessibility, system-monitor) that I have installed does not have any effect on session start up time.
Login to Gnome classic does not show the slow session start.
The system logs do not show anything suspicious. Thus, what is the best way to identify the underlying problem?