The Soviets famously used to licence typewriters and mimeograph machines. What brought down the Soviet Union wasn't internal dissidence and samizdat, it was external propaganda and cultural missionary engineering.

Even if an ISP shuts you off you can always use FIDOnet, or some equivalent. If censorship were ever likely it wouldn't take long before Internet gateways and servers started appearing in foreign countries that couldn't be censored directly.

The Chinese have been having an interesting time trying to manage censorship. It sort of works, but it's a long way from being airtight.

A more significant problem on blogs is astro-turfing. If it's done skillfully enough it's far more dangerous and far more influential than sledge-hammer censorship.

The CIA are notorious for the tradmed equivalent of astro-turfing. It would be naive to expect that they're not ready to do the same on blogs.

dKos is already rife with it. As soon as people start getting too critical of Obama, up pops a testimonial to his ineffable awesomeness on the rec list.