Just curious, i have a old USB mouse connected to my MacBook Air. I noticed that in the middle of the night (when the cover is closed an MBA is a sleep). The LED (red) inside the mouse is turned on for a few minutes (the mouse has transparent case, so thats easy to spot). I don't hear the fan, but certainly MBA puts some power on the USB port. After a few minutes is goes off again. I think it repeats a few times a night.
Anyone has a clue what goes on?