Keep an eye on Sidebark.  I think founder, David Cho’s, insight is spot on: privacy is about to become a Big Thing as Facebook, Google and pre-IPO Twitter become more aggressive in selling our data in order to justify sky-high valuations and consumers start to wake up to the consequences of allowing their data to be mined.  He is also right also right to assert that privacy should be the default feature for any social network.  Sidebark is currently only for videos and images, but there is no reason why a similar approach to broader social networking should not emerge, which will have enormous implications for the business model of Facebook et al.