Abstract the discussion from bitcoins to a USD/EUR transaction.
Exactly. Bitcoins should be treated identical to any foreign currency for any taxation reporting. Companies/individuals receive foreign currencies all the time and accounts know the rules for how to treat this under tax law. Bitcoin is no different for this purpose.
In college I studied the accounting rules for accounts held in foreign currency under FASB. FASB stands for Financial Accounting Standards Board; it is an international standards body. FASB is concerned with creating the rules that most accurately reflect accounting for financial purposes (for the benefit of investors). FASB does
NOT govern the rules of tax accounting, which is a national matter. For that you look to the IRS code. The IRS code, believe it or not, is shorter and less thorough than the FAS collection. Whereas the FAS collection usually has exhaustive prescriptions for every little issue endlessly debated at conferences (and people call us geeky!), the IRS code will tend to give some guidelines and then say "by any reasonable method". And then when you get audited, you have to convince the tax court that you were being reasonable. Guilty until proven innocent. (I am not making this up. The professors actually lectured on all this.)
In the case of foreign accounts, I believe the tax treatment is basically the same as barter transactions. You are required to estimate the value of your transactions in USD by any reasonable method. Since bitcoin is exchange traded, the exchange price would almost certainly be tied to any method considered reasonable, and whatever method you choose, it cannot change year to year and still be considered reasonable.