On the subject of 2.
People have speculated "could a government stop Bitcoin".
The answer is an unqualified "Yes", and the project will tell you the same thing. All it takes is having over 51% of the computing power of the world's mining operations.
A fork of Bitcoin called CoildCoin was killed by Luke-Jr. He explains his reasons for it a few pages into that thread, but basically he considered CoiledCoin to be fraudulent and/or a threat to Bitcoin. He claims he used only his own resources but its possible he used a large mining pool he operates.
Now the Bitcoin FAQ will tell you that there are a lot of limits to what you can do with 51% - little more than double-spending your own coins. That is enough though - once people know that the blockchain is corrupt they will walk away from it.
I've seen estimates that for only $80MM you could have an order of magnitutde more processeing power than the entire pool of miners that were operating at the peak last summer (many of who could come back online quickly). This puts the destruction of Bitcoin easily into the operating budgets of most Nation states, lots of companies and quite a few individuals.
Tangential, but a subject of some local interest:
Why Bitcoin will fail by Avery Pennarun. "The sky isn't red." Thesis:
I'm not sure I buy these and am not competent to evaluate his claims on 3., but would like others' critique.
L019: Bitcoin P2P Currency: The Most Dangerous Project We've Ever Seen by Jason Calacanis. A rather more enthusiastic viewpoint of the project:
The actual text contains many more caveats than the eye-catching selection of points above.