Facebook is now being destroyed by its overwhelming success. Since people feel locked in (because, hey, that's where all my friends are...) facebook can keep cranking up the heat, making the experience more and more unpleasant for users, and they will still stick around and give their eyeballs to it.
From talking to many people on and offline, it seems that facebook is almost universally hated now, but we have no choice, since everyone else is on facebook.
This will probably keep working for some time, but eventually, and very suddenly, there will be a tipping point where many people suddenly can't stand it any more. Once facebook loses that first big chunk, then not everyone will be on facebook anymore, and all the others who despised it for years but hung on because everyone else did will not have to put up with it anymore.
Facebook will suddenly go from universal necessity to irrelevant, and it will happen overnight.