Facebook after going with IPO, recently did an update on their comment section where they would have a complex algorithm to check if a content is appropriate or not. It is related to offensive, abusive, porn language content in your comment would show up a popup like this.
One good example that is going round is by Robert Scoble trying to add a comment and has got 500+ Google plus.
This is not the only control that Facebook has. There have been reports disabling accounts and other measures taken by facebook on accounts, which do not adhere to their policy. Coming back to inappropriate content the most word that is going around is it being very subjective. Being subjective is always in the eyes of who thinks that are positive or negative, So far the platform that you are working on sets the rule of it being positive or negative. I would believe sooner or later we should see these changes on other social network as well. All I hope that this censorship goes well and allow real time users to flag items rather than being stopped on making an appropriate comment.