I also just lock the device when I'm not using it. However, I have some doubts about the 'idle-mode' on the N800; when I go to bed, I lock the screen, asuming it's in some sort of power saving hibernation mode, but -sometimes- when I wake up the device is off and the battery is drained so it won't reboot as well. This happens when the battery indicator says it's more than halfway charged...

This doesn't happen when I leave the device on the charger at night.

I asume there is either someting buggy in the (hibernation?)-mode, or the device doesn't really have all that great power saving options