I am confused about what you two guys are debating. The best I can make out is Paul Rivers is pro dynamo hub charging and njkayaker says forget the dynamo and simply use cache batteries which can be charged from some external source.

I have a dynamo hub and usb charger that I use to charge an external battery pack with. I can then use the battery to charge other usb chargeable devices. Yes, I can go to a restaurant and charge the battery and not use the dynamo hub. In my opinion it is nice to make your own power so you don't have to rely on an external source.

There are many USB chargers on the market. A couple (B&M luxos and AXA Luxx 70plus) are integrated with the headlight, a couple utilize the fork steerer cap for the usb outlet, some have integrated batteries and some don't. I have a LightCharge which doesn't have an integrated cache battery but seems to work fine. My hope is that the technology improves and the price comes down because for long distance cyclists providing your own power is really innovative.