I have one of the old firewire/USB hybrid cables that Apple sells and use that for my iPod touch. It sucks to use two ports, but it's a necessary evil for me. I don't leave my PowerBook running all night, but I want to charge my iPod and not worry about having to disconnect it.
USB will charge and sync the iPod, but will NOT charge while the Mac is asleep. Some report that leaving it connected while the host machine sleeps will actually DRAIN the battery.
FireWire will charge but NOT sync the iPod. It will also charge while the Mac is asleep.
I have one of the old firewire/USB hybrid cables that Apple sells and use that for my iPod touch. It sucks to use two ports, but it's a necessary evil for me. I don't leave my PowerBook running all night, but I want to charge my iPod and not worry about having to disconnect it.
In Leopard, you can sleep your computer while your iPod charges and it works because I've done it. I have only USB cables, no FireWire.
My iPod's charge with USB during sleep (Intel iMac + 10.5.1)
I just tested this on my PowerBook and confirm that it still does NOT charge over USB while the PowerBook is asleep. It'll charge over firewire while asleep, but not over USB.
I think you need an Intel Mac with Leopard to charge over USB during sleep.