The biggest problem governments will have with bitcoin is the anonymity involved in transactions. They will point to money laundering and criminals using it as an untraceable  medium of wealth as the reason to shut it down. Without that they won't have leg to stand on in a court of law. You'd think there aren't any real money laundering operations to warrant gov scrutiny.

People should pay taxes on bitcoins. It's probably the only thing that can prevent a complete shutdown.