I needed to implement quick switch of currencies in e-Commerce web store.
I found plugin wp-e-commerce-multi-currency-magic, but it was pretty outdated – working only on version 2.7.6 of e-Commerce.
Version 3.8 had lot of changes, which did not work with this switcher.
I forked old one and started developing brand new currency switcher.
If you are interested – get it from here.