Isn't bitcoin explicitly a currency? I don't see any ambiguity around that. Or do you only get to be a currency if you're backed by a government entity that can be manipulated?
My perspective is that the real promise of Bitcoin is to be "successful" regardless of government regulations and categorizations. I know it sounds idealistic but I think if the Bitcoin community needs the US govt. to cooperate in order to be successful then it's probably not going to happen.
I guess "success" could be defined as widespread use. Somewhat stable (non-zero) value for Bitcoin would also probably be part of "success." :)
For many purposes, yes, it is, especially in tax law, which is why people also wanted Bitcoins to be recognized as such.
Under Subtitle A of the Internal Revenue Code, foreign currency like the Yen has special rules vis-a-vis commodities. In particular, when you buy something with Yen (up to $200 in value), it is not considered a realization of capital gains and so it is not taxable, unlike if you used a commodity to pay.