The IRS just ruled that Bitcoin will be treated as property. That means any transaction conducted with Bitcoin as currency could generate a capital gain on the Bitcoins traded, which must be reported. To obtain a value, the ruling says you have to check the current rate on an exchange at the time of a transaction.
So that could pretty much put Bitcoin out of business as a medium of exchange in the U.S. There is already an exception in the tax code for foreign currencies, which can fluctuate in value relative to the dollar between transactions. Why not Bitcoin? But there may be a reprieve: “…the IRS’ guidance may not stand forever. The Treasury Department should now begin developing formal regulations tailored to digital currencies.”