New: After digging around a bit more, I found out the problem is much more that the system is not suspending on its own, although suspending manually (shutdown->suspend) works well. I used the suspend after 5 mins setting on both ac and power from the power settings menu.
The only "solution" I could find for that problem was linked from another thread : http://thecodecentral.com/2011/01/18/fix-ubuntu-10-10-suspendhibernate-not-working-bug Did not work for me.
Old: If I manually (with gconf-editor) set sleep-inactive-timeout to another value other than the 5/10/3/1 from the power manager, the settings will be ignored (= no suspending at all). I set it to 10 and waited 20 seconds. Tried logging in/out and rebooting still the same. Also restarted (killed) the gnome-settings-daemon, still the same.
Am I missing something? If I understand it correctly the gnome-power-daemon (or whatever the name was in older releases) is now completely replaced by the gnome-settings-daemon. Or am I missing an additional package?
Here comes all my settings-daemon dconf-settings:
org.gnome.settings-daemon.plugins.power active true
org.gnome.settings-daemon.plugins.power button-hibernate 'hibernate'
org.gnome.settings-daemon.plugins.power button-power 'interactive'
org.gnome.settings-daemon.plugins.power button-sleep 'suspend'
org.gnome.settings-daemon.plugins.power button-suspend 'suspend'
org.gnome.settings-daemon.plugins.power critical-battery-action 'hibernate'
org.gnome.settings-daemon.plugins.power idle-brightness 30
org.gnome.settings-daemon.plugins.power idle-dim-ac false
org.gnome.settings-daemon.plugins.power idle-dim-battery true
org.gnome.settings-daemon.plugins.power idle-dim-time 10
org.gnome.settings-daemon.plugins.power lid-close-ac-action 'suspend'
org.gnome.settings-daemon.plugins.power lid-close-battery-action 'suspend'
org.gnome.settings-daemon.plugins.power notify-perhaps-recall true
org.gnome.settings-daemon.plugins.power percentage-action 2
org.gnome.settings-daemon.plugins.power percentage-critical 3
org.gnome.settings-daemon.plugins.power percentage-low 10
org.gnome.settings-daemon.plugins.power priority 1
org.gnome.settings-daemon.plugins.power sleep-display-ac 0
org.gnome.settings-daemon.plugins.power sleep-display-battery 0
org.gnome.settings-daemon.plugins.power sleep-inactive-ac true
org.gnome.settings-daemon.plugins.power sleep-inactive-ac-timeout 10
org.gnome.settings-daemon.plugins.power sleep-inactive-ac-type 'suspend'
org.gnome.settings-daemon.plugins.power sleep-inactive-battery true
org.gnome.settings-daemon.plugins.power sleep-inactive-battery-timeout 10
org.gnome.settings-daemon.plugins.power sleep-inactive-battery-type 'suspend'
org.gnome.settings-daemon.plugins.power time-action 120
org.gnome.settings-daemon.plugins.power time-critical 300
org.gnome.settings-daemon.plugins.power time-low 1200
org.gnome.settings-daemon.plugins.power use-time-for-policy true