Social networking sites self-destruct more regularly than depressed Bond villain lairs full of Mission Impossible messages, leaking oil drums and a drunken fire juggler.
Networking sites replace troublesome "meaningful relationships" with an easily-tracked number. Unlike friends, logging on doesn't require effort. Or showers. The instant it becomes possible to conceive over the internet the human race will start evolving backwards.
The precise moment a social networking site turns to shit is when the makers realise "Wow, we've got an army of millions of obsessives - how do we make money from them?" MySpace turned their entire site into a commercial break, Facebook lets anyone who can hit a keyboard two tries out of three poison the place with crapplications, and Twitter are just hoping the problem will go away/one of the team will find a treasure map.