http://fincen.gov/statutes_regs/guidance/html/FIN-2013-G001.htmlA user who obtains convertible virtual currency and uses it to purchase real or virtual goods or services is not an MSB under FinCEN's regulations. Such activity, in and of itself, does not fit within the definition of "money transmission services" and therefore is not subject to FinCEN's registration, reporting, and recordkeeping regulations for MSBs.
How a person engages in "obtaining" a virtual currency may be described using any number of other terms, such as "earning," "harvesting," "mining," "creating," "auto-generating," "manufacturing," or "purchasing," depending on the details of the specific virtual currency model involved.
It seems that a miner who uses the virtual currency they mine to purchase goods or services is not a money transmitter.
http://www.coindesk.com/bitcoin-law-what-us-businesses-need-to-know/Individual bitcoin miners who convert their “created” coins to fiat are money transmitters, even though they never act “as a business,” nor accept value from one person to transfer it to a third person.
Exchanging their mined currency to fiat apparently makes a miner a money transmitter (although you would think that if the miner is going through an exchange, that it should be the exchange that is the money transmitter.)
I'm wondering about mining pools. If the pool earns the coins, then later distributes them to miners, they would be money transmitters. If they simply facilitate building a transaction where the newly generated coins are distributed direclty to the miners without going through the pool (no inputs) then it seems they wouldn't be 'transmitting' to miners, but are just managing the pool sharing and providing a service.