Well... Here's the thing...
I think it's possible to censor the world wide web (www). But I think the concept of the internet is fairly likely to never get censored and/or shut down. I mean... Really, the technology that powers the web is like 30 years old now (at least the fundamentals are). So, if the US government, for instance, decides to start somehow censoring the net, suddenly graynets seem pretty appealing.
I guess the bigger issue is WHY would the web start getting censored? I mean, China censors the web because they don't want their people to learn about things before the chinese information office gets a chance to spin things their way. In the US, about the only thing that's truly censored is pedophile porn, and I think we can pretty much all agree that's a pretty good thing.