XMPP seems to be a better protocol on which to base such a [higher -level] protocol. There are a couple projects following this path, but both seem to be a bit timid about trumpeting their own horns. I have nothing to do with either of them other than silently hoping they eventually win the day:

1) http://onesocialweb.org (Not sure about their future)

2) http://buddycloud.org (some of their contributors are HNers, but even though they're recipients of Google Summer of Code 2012, they are also quite modest).

These are the approaches that seem to be the most promising to me, even though their use of XMPP has been disparaged as non-developer unfriendly. I simply disagree, as a non-developer (though I am working to change that; I've got simple Django and Rails up and running on my LAN).

I believe the ideal hardware for such a project is:

~1.2GHz ARM CPU

-4GB RAM

-64GB SSD

-2x SataIII HDD (~6TB RAID)

-on a consumer ISP connection with 250GB soft cap