Federation
Maybe I'm weird, but I'm not here because of the cool design (more like in spite of it if you think about #single_post_view). I use #Diaspora and other #federated #socnets because of #federation.
Control Your Info
To me, federation is a way to restore control of one's information and communications to that person. The promise of federation is that one day soon, you and I and our friends and families will either host our own (social network, instant messaging service, mail server) or we'll be able to have someone we know in our local communities host it for us.
Perverse Incentives
Right now, big, centralized networks get more attractive when they have more of the people you know (or would like to know) using them. And so, big networks get bigger and more intrusive and invasive, and they collect more and more data to sell to advertisers and government agencies, and yet, because all your contacts are using those networks, you more or less have to use them. Economists would c...