Basically, it mean that exchanges coming to the U.S.A. will have to keep a book of transactions. However, I don't know yet how the U.S. want to track the whereabouts of a company. They know when they exchange Fiat->BTC, but then what? How will they perceive any taxes after that? I could just transfer 1000$ to BTC and say that I bought something with, when in reality I hoard it and it double value. I also guess that when Bitcoins is more mainstream, a lot of companies will just directly trade in BTC. Instead of receiving 100M for something and having to cover and transfer to fiscal heaven, then they will just ask to be paid in BTC, unseen, under the radar.
So, this draft is a basic protection, but they ain't much the U.S. or any government can do apart from controlling the Fiat/Bitcoin conversion points (i.e. the exchanges). As said, once more mainstream, and we get
paid directly in Bitcoins, then exchanges will be for medium/small players only. Big corporates will trade between them in Bitcoins, and trade a LOT more, a LOT faster, and a LOT more anonymously.