P2P and server-centric approaches to content & social networking

After talking to Daniel Harris of Kendra at Monday's Micro Content dinner, I've been pondering the issue of server-centric versus P2P approaches for a next-generation solution for content and social networking. Could we have the best of both worlds, where users can connect directly to one another on one hand, but may also route that connection through the self-consistent data space of semi-closed sub-networks (such as i-together) on the other, utilising a Kendra-like meta-data exchange protocol as "glue"? Could the "intelligence" of a central server (in terms of tracking the network's content and connectivity) be virtualised in the nodes of a pure P2P über-network, or would it be necessary to integrate "hub" servers into a P2P fabric? Digital Identity comes into the picture here, too—presumably an area that the Kendra initiative could embrace—as having a (1) reliable and consistent way to identify users and their personal information across the über-network that (2) at the same time expresses the aspects of users' identity that are specific to their presence and organic interactions within any given sub-network would seem to be crucial. FOAF and other intiatives I've come across (currently) focus on (1).