Evidently, many hoarders/speculators decided to cash out at once -- much like the audience in a movie theater would try to go through the exit door at the same time if someone were to yell "fire!" The naive souls who recently bought bitcoins to make a 'quick buck' are in for a rude surprise. In the short run, no one knows how Bitcoin's price will fluctuate. In the long run, however, if Bitcoin continues to work as in…
It doesn't matter if they can't enforce it 100% (or even 1%). What matters is that it will kill almost all opportunities to use it as regular money for legitimate purchases by major companies etc in the future. And that it could also land your ass in jail (with ISP monitoring and such being what it is).
Why would a government do that? For one, because they don't like money systems they can not control. Second because they would argue it can be used for money laundering and such.
Time and again it has been proven that you cannot solve social issues with technology. For example a solution for private communication exists: cryptography. And yet, the government can limit what kind of cryptography you can use in your app or export, etc. And they can even throw your ass in jail if you have an encrypted file and you don't hand them the key. You have to go all the more deeper, and even that doesn't solve the issue of your dumb cousin exposing your secret in his plain text email to you.