Dear Matt:
I work for a company Bike2Power, and we sell bicycle USB charger kits for smartphones and iphones called SpinPOWER Kits. It is a bike-mounted charger for USB-chargeable devices that uses a bicycle dynamo. Incidentally, our charger is now being tested by a RAGBRAI rider. If you are interested, please contact us and I will connect you with him so that you can obtain his feedback directly. So far, he is pleased with it and wants to take it to the RAGBRAI with him.
Julia
http://www.bike2power.com
info@bike2power.com