By the way just a note from Tim Berners-Lee on this exact topic, updated
4th June:
"Users are given, instead of a username at each SNS, a single URI, or in
fact one for each persona they want to have. (Ideally, this is a WebId,
which uses the foaf+ssl scheme, but an OpenID could be used and linked
in as OpenIds are already deployed to a certain extent, and there is
discussion of other schemes. *There is [2010] future standardization
work to be done here.*"
[1]
http://www.w3.org/DesignIssues/CloudStorage.html
@mattl know you're ultra busy right now with house move etc. ... but would encourage you to touch base with Tim in Boston, if you get the chance, as he's really been thinking about this [social] problem for 2 decades, and is focussing on it hard in the last 1-2 years. I think a 15 minute chat on the subject would be extremely valuable in terms of how to architect things to interoperate at Web Scale.