As dataportability.org describe it: "Data portability enables a borderless experience, where people can move easily between network services, reusing data they provide while controlling their privacy and respecting the privacy of others." Simple video explaining the problem and potential benefits.
DataPortability – Connect, Control, Share, Remix from Smashcut on Vimeo.
The three elements are connect, control, share, remix. While I agree with the first three, I think the idea that one social graph can be transported to another site is wrong. I would not want to mix my Linkedin social graph with my Facebook graph. So for me assuming they can solve the first three elements the crucial one will be how you control and remix the elements of your social data.
