I installed gnome-shell and ubuntu-gnome-desktop on top of Ubuntu and now the automatic suspension doesn't seem to work (I've been using GNOME now for some time and I'm not 100% sure if it worked at some point). Also if my laptop is on battery power, the screen will dim after ~45 seconds like it should.
On Unity the automatic suspension works fine.
I wonder what service GNOME is supposed to use for power management? At least Upower.service is running according to systemd. Or is there some way to determine what programs inhibits the power manager from putting the system to sleep?