In theory, it wouldn't be difficult at all for your own ISP to implement such blocks on content that you view. (Though I realize they are talking about a country-wide block on certain content)
For the average user, they wouldn't even know if they were being censored. For example, take a new website with the url newsite.com that an unsuspecting user has never viewed before, but has been deemed controversial by many. They stumble upon the url on a message board such as this one and upon clicking on it, they are redirected to a different website, either related or unrelated to what they think they would be viewing.
I'm fairly confident that the average user wouldn't realize what's going on if an ISP were to in fact put into place such restrictions.