Why are they on?

Somebody also might wish to look at why users leave their PCs on overnight in the first place.

'round here it's because the centralised admin types load them with so much admin and monitoring crap that fires up at boot time that it takes the older ones 45 minutes to boot and login. So, unless you enjoy an hour's runthrough of the XP boot process every day, you leave the thing on.

If their admins are anything like ours, they may save 40,000 quid in leccy, but they'll lose millions in productivity.

TeeCee