Thanks for the replies - much appreciated.
I've attempted charging my 7100g from a PC without the drivers. No go unfortunately. Ugg, I tend to agree with you as well - the only explaination I can come up with is that the BB can negotiate with the charger, or there's some subtle hardware difference.
I'm thinking I will have to buy a BB USB wall charger - one of the ones with a USB port rather than the mini-USB plug. Basically, I'm going to be charging a BB, an MP3 player and AA batteries from the same USB outlet while I'm travelling (not at the same time, obviously).