The real problem is one of changing policy and retrospectively. Mt Gox got the account when bitcoin was next to worthless. The government paper work has no provision to post an up date or write "this may become money at some time in the future."
There's a good chance FinCEN has blown a police sting or two. The system is pseudonymous and block chain is public. With the skills you could track your buy through silk road to the guy making the LSD.
http://www.reuters.com/article/2011/06/15/financial-bitcoin-idUSN1510930920110615There is provision for additional data in a bitcoin transaction message. This means Satoshi even anticipated this problem. However the libertarians will have a fit if anyone implements it as anti-money laundering transaction tags.
