heh I think we all learned that the first few nights we had our iPods.
For some reason, the iPod touch won't charge over USB while the Mac or PC is asleep. My PowerBook will charge over firewire while it sleeps, though, so that's what I do. I have the firewire wall charger, too, so I also use that.
If you use any powered accessories, such as the iHome dock/stereo thing, it will charge even while the computer is off.
I personally use an older Belkin Tune Sync which is a dock / four-port USB hub (complete with AC adapter) so it charges when my ipod is connected whether the computer is on or not.
Yea Im pretty sure my macbook charged my ipod Touch overnight while it was sleeping. Thats the only time I charge it. and i am listening to it right now.