in response to one lawschoolblues

can US block an IP address from the whole country?
if I may quote davmoo(my hero this hour for stating this to perfection)
Theoretically in answer to your question, yes. In actuality, it would never work.
now supposing that it did the reverse is also a problem.
the us sets up an ip block for registered casinos and i dont want to register my ofshore casino with them but i want my ip address to appear as though it is within a given range(Active spoofing)

could all ISP's cut off a particular IP address?
this is akin to asking can all 7/11's carry jolt all the time? sure they can you expect them to still because of unforseen circumstances my 7/11 is joltless. take a look at the FBI's carnivore program and how it worked or didn't.
plus some isp's would simply disagree with such filtering like XS4ALL.

The closest thing currently to blocking on a massive scale like your talking about is what happened in china.

There was a great panel on How it all works and how it is circumvented that I saw at The Fifth H.O.P.E. that you can stream or download

"How the Great Firewall Works
-Bill Xia

L
L

China currently puts in the most effort to censor information on the Internet. Bill was first involved in freenet-china and started DynaWeb in 2002. He has developed a thorough understanding of China's Internet censorship technology ranging from IP blocking to DNS hijacking etc. Various techniques have been implemented to get around them. There will be an explanation of a censorship algorithm never before publicly released as well as a live demo on how it works. Time permitting, an analysis of how the Chinese government uses information control on its people will also be presented."

but i'm sure with the right words or backers you could convince the government to modify there existing isp boxes to add somthing that they would think would work or just convince the government that it all could be done thru the existing DNS system. Most of the people in places of power Judges, Congress,exc. Dont have the passion or time to know any better.

People are unhinged in learning that most all of it is "security theater" rather than the myth security. for example why have plastic knives on airplanes if your gonna give me a metal fork and do you know how to open your door non destructivly without a key?

theres 100's of hours of audio and video on all this stuff linked from 2600 for the latest news check out hackwire and the wikimedia projects