USB vs Bluetooth mouse

Along with one of those lovely new 12" iBooks, I'd like to get a mouse. I love the convinence factor of a bluetooth mouse - just turn it on and go. I'm not going any heavy gaming or graphic design, so minor lag isn't a factor (so long as its MINOR). My real question is: is there a difference in battery consumption when using a bluetooth mouse vs a USB mouse? If I went USB, I could turn off airport and bluetooth when not in use and preserve battery power. But the USB mouse is going to drain the main battery anyway whenever it's plugged in. The bluetooth mouse powers it's own LED, but has the overhead of bluetooth. Argh. They probably just cancel each other out, and my guess is that we're only talking seconds of extra battery power if there is a difference, but I was wondering if anyone had any experience with this scenario?

To sum up: Anyone notice a difference in battery drain when using a USB mouse vs a BT mouse on either an iBook or a PowerBook?

Thanks