Eexcellent Post by Ben Werdmuller (of Elgg fame) suggesting a place for both distributed and centralised social network architectures because the use cases for each approach are different.
Address of the bookmark: http://benwerd.com/2010/06/building-a-distributed-social-network-youre-doing-it-wrong/
I am a professional learner, employed as a Full Professor at Athabasca University, where I research lots of things broadly in the area of learning and technology and teach mainly in the School of Computing & Information Systems, of which I am the Chair. I am married, with two grown-up children, and live in beautiful Vancouver.