Hey Mark Pincus, I agree with you ("that there is a need for a portable reputation system that can enable non-ebay p2p transactions"). You didn't link to anything by Auren Hoffman who is working on this, so I thought I would point people to ClipperZ -- they are combining Identity 2.0 (using existing systems) and building distributed reputation managers on top of that.
And of course, "transactions" is a very general term. Identity is to figure out that you're talking about the same person, profile information gives you some contextual information about that person, and reputation lets you know (again, in context -- relating to you and your connections) whether you should trust that person.
Mark goes on to say:
My own experience has been that its a major uphill battle convincing walled garden sites that benefit in the short term from lockin to act in the long term interest of their users.
This is the sticking point. Many of the large "containers" of identity, profile, and reputation information do not have much of an incentive to open their networks. The one thing that might challenge such silos is the rise of large amounts of federated networks. Even here, when the network is small, it is difficult to convince people to federate -- who will be the hub or aggregator of the network? Everyone will want to be in this central position, and we are back to hubs facing off against each other.
This is the beginning of an exploration of how these concepts fit together. I hope to explore them in more detail at the Internet Identity Workshop (Phil Windley just posted Who's attending on the wiki).