The most they can do is outlaw exchanges, and it would take *all* governments to cooperate to have any effect. After that bitcoins would go to the black p2p underground market, that's all.
The black P2P underground market means very slow transactions, which would kill one of the most desirable aspects of Bitcoin as a purely digital currency. Like I said, if the gov't decides to crack down on it, it won't survive as the Bitcoin we're used to and its price will definitely take an immense hit.
But yeah, I hadn't read about the FinCEN ruling or whatever kind of act that was, when I last posted on this topic. At this time I'm somewhat less pessimistic about Bitcoin's future, though still worried that its protracted survival will unnecessarily delay the adoption of a truly well designed digital currency system that would be based on sound economic concepts (not just a cryptographic toy invented by some random programmer) that could really be a worldwide substitute for all fiat currency systems.
there's no need for regulation. The market will take care of itself.
You must not be from the same planet as the rest of us.