[a1a]

I think they are just splitting up trust to less trust-able entities. Sure, the impact of a malicious entity would be less severe, but the chance of any being malicious is rather big. Cause let's face it, my mom is not going to run her own server, and I believe she has the right to control her data as well as all of us do.

I believe the only way to properly implement a social network is not to trust anyone but your friends. I'm thinking something like a freenet-like apporach, everybody in the network holds a little bit of encypted data, but only the ones you have accepted as friends will be able to see your data unencrypted.