I foresee some of the resulting networks, if public enough, being a mirror of linkedin, with people in certain industrial/academic circles just parroting each other and rejecting everyone else. lol.. At least to begin with, though that might change over time.
I imagine the majority of data will be kept private though, no-one wants gangs of unknown thugs turning up at their doorstep to convince them to change their stated public position on particular topics!
A big difference in a p2p system is that you can eventually tune out the sources you don't trust.
Absolutely, yes, though it can get complicated quickly!