Well, I own a teletype Bluetooth GPS unit and I am quite pelased with it. Its going on two years old.
Tired of buying batteries or having to recharge the unit, i figured on modifying it to take power from a usb port.
Attached are the images.
The advantage is quite evident to me. the device can now use power from:
battery (rechargables die out after a while)
dc wall plug (running on an inverter in the car... who wants to carry an inverter?)
cig plug (which i didnt have at the moment...)
usb plug... (i have ports up front on my dash,, might as well!)
I no longer have to rely on an inverter.
I have not actually finished it, but its working.

Im trying to figure out a way to make the wire detachable... probably a molex connector of some sort, and stash that into the battery compartment.... hmm...
The wire of the device i used was a usb clip on lamp.