I have 3 systems running Karmic. 2 are clean installs, one is 64 bit, the other 32. In both of those power management works correctly to shut off the monitors.
My 3rd system is an upgrade from Jaunty. It is 32 bit running on an AMD tripe core with 4 gig ram and nvidia 8600GT using the Nvidia 185.13.36 driver from the Hardware Drivers utility.
This system is on 24/7 and I have the screen saver set to trigger after 5 mins. and then power manager should shut off the display after 10 mins. It functioned correctly in Jaunty.
After the upgrade to Karmic release candidtate, it continued to work correctly for a few days and then the power management stopped shutting of the monitor. The screen saver kicks in as expected, but the monitor never goes to sleep.
System monitor shows that gnome-power-manager is "sleeping".
If I issue the commands :
it will work correctly as long as the terminal window is open.
I also found if I killall gnome-power-manager and then log off and back on, it will work as expected, but on a reboot, it returns to its non-working behavior until I kill it and log off and back on.
This behavior is very consistent and happens on every reboot.