I remember years ago, hearing that computers consume more power by frequently starting up and shutting down than it would take to just let them run all day.  I think the number I heard back then was 3 -- if you're going to turn the computer on and off three times or more over the course of the day, you'd be better off just leaving it on.

Does anybody know if there is now, or ever was, truth in that?  I checked Snopes, but couldn't find anything, and I'm just not sure who else to ask...