A lot of things that have happened since 9/11 in the U.S. would have been laughed at as unlikely before the event.  Suspension of the right of habeus corpus for suspected terrorists, even if they are U.S. citizens, for one example, but there are others.  Incrementalism is insidious, and for those times when there are significant objections to some new usurpation of individual rights by the government, there is always a convenient "event" which facilitates the acceptance of new restrictions "for everyone's safety."  So long as people consider life (and by extension safety) their #1 priority (ahead of freedom, honor, etc.) then there is no reason to believe this trend will not continue until we have no meaningful rights left (compare, for example, the U.N. Universal Declaration of Human Rights to the U.S. Bill of Rights).

"The whole aim of practical politics is to keep the populace alarmed (and hence clamorous to be led to safety) by menacing it with an endless series of hobgoblins, all of them imaginary."  H.L. Mencken (written around 1918)

As those of you in the IT business already know, any approach at regulating the internet that operates on the basis of restricting individual ports or IP addresses is doomed to fail, because the "hackers" will respond by simply randomizing the ports used, or changing IP addresses.  Similarly, any attempt at using deep packet inspection will likewise fail because the hackers will respond by using encryption.  The only way for governments to stop pesky anonymous publishing services (freenetproject) anonymous network services (i2p), anonymous currencies (bitcoin), etc. will be to make a fundamental change in their approach.  Instead of the inherently promiscuous approach of allowing everything except certain services/sites, the opposite of denying everything except that which is permitted will doubtless be strongly pushed as the only way to control "child pornography, terrorism, and hacking" on the internet.  This won't affect the average person who uses the internet to order goods from Amazon or to check his credit card balance online, but it will affect those of us who bridge networks with ssh tunnels, utilize overseas VPNs to gain access to services not available in our own countries, use bitcoin/freenet/i2p, etc.  As with everything else, exceptions will always be made for larger corporations with "legitimate" communications needs, but that won't be very helpful to most of us.

I'm not claiming the above is inevitable worldwide, just reasonably foreseeable, and perhaps likely on a more localized basis.  It would be nice if it were possible to provide mechanisms by which bitcoin could survive in such an environment.  Any solutions would need to rely on the inevitable information leakage that will always be present in any worldwide communications network regardless of the best efforts made to limit it.

The ultimate fallback mechanism of manually transporting the necessary files to update one's bitcoin data directory would be a great start.  If some easily-followed procedure of accepting updated blocks in file form (either as email attachments, from a USB-key or from a file extracted from a steaganographically encoded MP3/JPG file as already suggested) were created, then many forms of human ingenuity could be utilized to keep the network alive in the face of totalitarian regulation.

Automated mechanisms would need to be carefully considered because they tend to be predictable and thus detectable/able to be censored.  However, friendly web sites would offer one possibility, although they are easily blocked.  Those of you old enough to remember analog modems/usenet ! addressing/bbs will also see that the phone lines represent another possibility.  Speaking of usenet, if it were allowed to continue in its current form (seems unlikely), then it also represents an ideal medium for block updates to propagate.

A plug-in mechanism added to the bitcoin client, through which plug-in modules could be developed on an as-needed basis to adapt to potentially rapidly changing legal conditions seems like an ideal place to start.  The plug-ins could support various mechanisms for updating blocks ranging from manual updating with files to dialing into a remote computer using an old-fashioned modem, to accessing a radio-operated BBS on an amateur satellite orbiting the earth.