That ReX is kinda clever.
A while back I had an idea for a rechargable keychain light that would primarily be intended to charge via USB power.
It was actually made in 2005:
http://www.engadget.com/2005/05/10/ion-technologies-flashlite-usb-thumb-drive-with-flashlight/ Some available on Amazon now. Like this Victorinox for example:
http://www.sureneeds.com/5301g2.html