Interesting study of message deletion censorship
This article from Threatpost discusses a study out of CMU of Chinese censorship of their home grown social networking websites.
Now that they are blocking most of the western social media sites entirely, the focus of censorship is internal. Obviously blocking the internal sites as well would defeat the purpose, so they are selectively deleting posts instead. This study looks at the rate at which posts with sensitive key words are removed from the services.
It clearly shows how censorship can be taken to the next level when the censor controls the websites as well as the network.