I don't think that answers my question on intermittence, persistence and syncronization.

I can have my date hosted, but if my friends don't (that's why they use your service, so not to have to do that, or else they remain with Facebook, LinkedIn, etc. That's your USP), I can only access their data when my friends devices are online. Or, alternatively, you store my whole friends graph on my device, which presents scalability and performance issues. Or, 3rd route, you store my friends data on multiple devices on the network, doing "multiple seeds". Again, we're back to "opps my data is all over the place", when your Unique Selling Point was P2P = privacy, no need to centralize.

Even Skype Supernodes don't solve this issue. They solve some of the routing issue. Not the "address book/data issue". You don't seem to solve it either.