Speaking of MySpace, part of the reason for its downfall was the lack of privacy compared to Facebook back then.
MySpace had three key issues:
1. It had become a critical delivery platform for viruses, because their self-serve advertising model was a nightmare waiting to happen.
2. NewsCrop never really knew what the hell to do with it. So, they opted to try to use as a straight promotional platform in the old media model.
3. MySpace was the epicenter of bad design. It had become GeoCities 2.0.
Facebook will hold on a lot longer against any new competition because Facebook doesn't look like a dog chewed on it then barfed it back up.
If Facebook has a downfall, IMO, it's that kids and grammas seem to be co-existing in the same space. Strangely, this does not seem to bother the current batch of kids. But, if a tipping point is achieved, and Facebook becomes essentially the web version of CBS (US TV network notorious for have a geezer audience), and a viable, youthful competitor comes along, then Facebook would see serious erosion.
As-is, nothing of the sort is playing out.
Facebook's really big flaw is that advertising conversions from FB are practically non-existent. But, major internet properties can last a long time without a real business model. Look at Twitter's refusal to die, despite not having a real business model or any actual human beings using it (PR/marketing people and celebrities/wannabe celebrities don't count).
I never understood why people obsess about Facebook vs Google. Facebook has largely been eating up those parts of the internet Yahoo and usually one other company once controlled (email, games, personal web pages). None of this poses an existential threat to Google.
Google, frankly, sucks are anything that requires a quality user experience. Google is great at simple, straight geek tasks. Need to find a web page? They got that. Need to match an advertiser unit to a publisher unit and monetize it? They do that well. Want to provide easy access to all your friends' photos? Oh, man . . . Google will burn that shit to the ground.
Google is like the anti-Apple. It's incapable of moving into any part of the user space that requires more form than function.