A critical success factor for Facebook, which is almost as ubiquitous as e-mail now, is to keep annoying junk messages off our news feed. I very nearly gave up with Facebook due to drowning in irritating updates of friends' activities in Farmville, Mafia Wars and assorted horoscope games and I know several who did leave. Of course you can easily switch off these updates but new ones keep turning up. However, according to an article on CNN, How Facebook killed (most) spam, there are new and painless methods for minimising the amount of irritating messages you receive.
Facebook evidently track how we react to different posts. If millions of people hide certain updates then Facebook will block them and notify the company responsible. If the company is concerned about its image they will find another way of spreading the word on Facebook. It becomes a sort of self-regulation since the responsible companies want people to like them. The problem is that the real spammers don't care what we think of them and will just keep pumping out the digital sewerage. Facebook will have to keep working hard to block the social spammers.