Full disclosure. I am a front-end developer working with others on Blockstack Decentralized Open Source software.
Although P2P systems seemed as though they could solve problems like decentralized identity, which in turn could have actually put a world of hurt on FB, the limitations of the system itself prevented it from any real world authentication applications.
With a truly decentralized system, that utilizes the blockchain, users can now own their own identity. With this new breakthrough tech, Blockstack (http://blockstack.org), users now possess their own data and cannot be tracked. This puts FB, and other companies that rely upon advertising (tracking) as their main source of revenue, in a very tough position.
Now that there are applications and projects being built on Blockstack tech, I strongly feel now that it's only a matter of time before a breakout social app, or FB killer, will hit the mainstream.
Join the Blockstack community http://chat.blockstack.org