However, The fact that it's used as a form of currency is just an interpretation of what Bitcoin is. There can be other interpretations for what bitcoin-type system can be used for, for example Namecoin is used for name registrations. The judge declared that bitcoin is money by making an interpretation.
If anything, Bitcoin is just software. It will be very difficult to regulate.
1. Software using encryption is protected speech (http://en.wikipedia.org/wiki/Bernstein_v._United_States). Regulating bitcoin as in bitcoin the software would be a form of censorship.
2. Bitcoin uses many of the standard principles of cryptography we already use in e-commerce. Banning cryptography would have enormous consequences for the economy of the internet in general.
3. Banning or regulating p2p would cause an uproar.
4. If buying bitcoins in exchange for dollars is really exchanging a string of bits for money, then if this is banned or regulated, would it also ban buying software or other digital goods for money?
5. The regulations can't be too broad, but can't be too narrow. Would the laws restrict only bitcoin as a currency or other applications of bitcoin as well? If too broad, then they will unintentionally restrict other uses of bitcoin too. If too narrow, a new system will pop up again.