Looks very interesting. I think there is some ambiguity with respect to currency symbols, $ converts to USD and £ to GBP. However, depending on user location those symbols can be used to mean very different currencies.
Is there anywhere else that uses "£"? I didn't feel great about having $ default to USD but it is probably what most users want. I'll probably make it location-aware and/or allow the user to decide which it defaults to in the future.