In Europe, you must state your prices in the national currency. Conversion takes place at the moment of payment. If you officially include bitcoin in your accounting, it is treated (in Austria at least) as a foreign currency. You must document when, which invoice was paid, with which amount and at which exchange rate. And yes, only real thoroughbred bitcoiners do this work here. 😉

waaat @semisol operates a relay (in Europe) and states prices in Bitcoin.