I found the advisory
http://fincen.gov/statutes_regs/guidance/html/FIN-2013-G001.htmlAnd I quote
A user of virtual currency is not an MSB under FinCEN's regulations and therefore is not subject to MSB registration, reporting, and recordkeeping regulations. However, an administrator or exchanger is an MSB under FinCEN's regulations, specifically, a money transmitter, unless a limitation to or exemption from the definition applies to the person. An administrator or exchanger is not a provider or seller of prepaid access, or a dealer in foreign exchange, under FinCEN's regulations.
and the definitions of user, administrator or exhanger
A user is a person that obtains virtual currency to purchase goods or services. An exchanger is a person engaged as a business in the exchange of virtual currency for real currency, funds, or other virtual currency. An administrator is a person engaged as a business in issuing (putting into circulation) a virtual currency, and who has the authority to redeem (to withdraw from circulation) such virtual currency.
Draw your own conclusions but it seems clear to me that unless you are in the business of buying / selling or exchanging bitcoins then FinCEN clearly does not apply.