Facebook was an elite product, it required an Ivy League address just to get through the door and established a set of middle-upper class brand credentials. Facebook is now the default, it's full of crappy games & dodgy ads. Every shitty website has a like button. It's has an irremovable reputation for a lacadasical approach to user privacy. Everyone and their grandmother are on there, FWD:FWDing Glen Beck nonsense and Farmville requests.
Every market has stratification, we define ourselves by our brand associations. There is a hole where there should be the Mercedes, the Apple of social networks to Facebook's Dell. All that's needed now is something new to come along that woos the elite and Facebook's long term fate it sealed. There's a chance it'll be Disapora but there's a very good chance it won't.
That's not to say it won't be around for years to come but it has, to used a hackneyed phrase, jumped the shark and the difference is that Facebook's value comes from it's userbase, not its services or technology. Once the top end start bailing the rot will set in fast, momentum shifts with dizzying speed on the web. I've been thinking about this for a while, I figure if I'm right, I'll be able to point to this in a year or two and smile. Not quite as profitable as shorting FB but hey, it's just speculation for fun.