I would suspect that 8 hours idle consumes less power than 8 hours off followed by the vibration & other actions on startup.

My N900 is off-network overnights, but plays clock chimes every 15 minutes. The battery graph shows no discernible power use overnights if there are no phone calls, etc. But if I have to turn off then re-start the phone, the battery graph afterwards clearly shows a reduction in battery reserve.