It's a huge myth that Bitcoin is beyond the reach of governments. There are three reasons for this.
First, Bitcoin isn't actually decentralized. It's not a true open-source community of developers; the core group is tiny, and few others are knowledgeable about the protocol, which is poorly documented. Remove the mainline client and you'd destroy Bitcoin. The exchanges are hugely centralized. Exceedingly few people use Bitcoin for anything else other than buying and selling dollars, and there's only one place to do that in any volume - an unregulated Japanese exchange of questionable legality.
Second, Bitcoin is extremely vulnerable to denial-of-service attacks, both network-based (even the original developers were aware of this) and as a result of the higher-level Bitcoin protocol itself. The best analyst on these matters, someone using the label "ComputerScientist" at, among other places, Ben Laurie's blog (links.org) estimated that it would cost less than $1 million to topple the system without even any cleverness - just by obtaining a majority of the "legitimate" hashing power of the network.
Third, though this is more speculative, most people don't like to engage in financial crime; it's not psychologically the same thing as downloading a CD or a television show. Nobody thinks they're supporting significantly illicit activity by downloading some music that otherwise would have cost them $7. People can be easily persuaded -- rightly -- that they're supporting money laundering, significantly illegal and immoral purchases, and so on using Bitcoin. Indeed, because Bitcoin is essentially unneeded for legitimate transactions (and probably can't compete in the long term on transaction fees with other legitimate payments systems), its primary use aside from speculation is currently illegal activity, and there's no reason to think that will change.
First, Bitcoin isn't actually decentralized. It's not a true open-source community of developers; the core group is tiny, and few others are knowledgeable about the protocol, which is poorly documented. Remove the mainline client and you'd destroy Bitcoin. The exchanges are hugely centralized. Exceedingly few people use Bitcoin for anything else other than buying and selling dollars, and there's only one place to do that in any volume - an unregulated Japanese exchange of questionable legality.
Second, Bitcoin is extremely vulnerable to denial-of-service attacks, both network-based (even the original developers were aware of this) and as a result of the higher-level Bitcoin protocol itself. The best analyst on these matters, someone using the label "ComputerScientist" at, among other places, Ben Laurie's blog (links.org) estimated that it would cost less than $1 million to topple the system without even any cleverness - just by obtaining a majority of the "legitimate" hashing power of the network.
Third, though this is more speculative, most people don't like to engage in financial crime; it's not psychologically the same thing as downloading a CD or a television show. Nobody thinks they're supporting significantly illicit activity by downloading some music that otherwise would have cost them $7. People can be easily persuaded -- rightly -- that they're supporting money laundering, significantly illegal and immoral purchases, and so on using Bitcoin. Indeed, because Bitcoin is essentially unneeded for legitimate transactions (and probably can't compete in the long term on transaction fees with other legitimate payments systems), its primary use aside from speculation is currently illegal activity, and there's no reason to think that will change.