Chris Saad injected the data portability meme into the flow and suggested personal Access Control Lists, in the form of a “Sharing OK/Not OK” check box on data you give to individuals or companies. It would be interesting to watch Robert Scoble manually configure a complex ACL on his 20,000+ friends (Scoble rushes in where Angels fear to tread).
While it would truly be torture to force a person to manually configure an ACL for 20,000 people, it doesn't have to be that way. One wrong move, and you've lunched everything.
Giving away capabilities on the other hand would be a much easier thing. You have the host environment generate a capabilities token for the piece you wish to delegate access to, then send it through email, or on a web page, or whatever the end user's security policy specifies is the right thing to do.
It would make far more sense to have a system that lets users delegate capabilities to any given part of their information, blog posts, photos, etc. The fact that you start with a model of least privilege means that you start with the most you're willing to give away, and pare down from there. You don't have to worry about giving away the store by mistake.
Yes, Access Control Lists would be punishment, but being able to give away little bits, without fear, is a quite liberating alternative.
I look forward to the future.