I'm with Moab on this. From my recollection of economcs, the term that people should be using is a *Fiduciary* issue currency. This is a currency that is not backed by any commodity, but is also not necessarily by government decree or fiat.
Moreover, bear this in mind, most government "fiat" currencies are "legal for all debts both public and private". Can you pay your taxes with bitcoin?
Although you could argue that bitcoin is a de-facto currency, you could just as easily describe bitcoin as a "digital good". I could barter my not-valid for tax, not backed by anything digital "good" for another digitial good, service or real world good.
You may also want to look into the BIS (bank of international Settlements). They decide if a currency is "recognised" by the various central banks for trading around the world. Banks are unlikely to accepted it since it is an anethema to them; banks make their money by having the *monopoly on the creation of currency and the interest derived thereof*.
I'm nore sure if you are aware but the nascent stages of bitcoin came out of the anarchist community, here is the original article by Wei Dai.
Also the author of bitcoin in his paper who acknowledges Wei Dai,http://www.bitcoin.org/sites/default/files/bitcoin.pdf
posits one of the uses of bitcoin is to *avoid going through a financial institutions*.
In other words bitcoin is *political*. In a sense bitcoin is the "garlic" to the blood sucking vampire banks/big government. As a lawyer though I expect that financially (at least in dollars:P) it would be best for you to side with the banks to see how you can either tax or regulate away innovations such as bitcoin.
Despite being bitcoin being international, the banks exert significant influence on governments world wide though their existing debt based ponzi currency which they loan to governments, and harvest the interest back via tax. Being able to *avoid* the banks currency, and governments unfair taxes by using a third party currency will not be exactly popular with the ruling olligarchies. Note people are not doing anything *illegal* ....YET. By using bitcoin they are simply voting with their feet for a better system.
Maybe after you graduate you can help stop this by drafting laws to make up new crimes; if you represent the "right" interests this could be very profitable. Since you are in the US, I'd not be suprised to see the "Patriot Act" expanded to brand more harmless people as "terrorists".
In a nutshell, bitcoin is not a "toy", some people see it as a *political tool* to reduce the power of overbearing, bloated central governments and the associated banking olligopolies.