The portable social graph is only a special case of portable profile data as dealed with (to some extent) in FOAF. Portable profile data is only a special case of any user-generated content locked in Web 2.0 applications. What is needed is a private content system that hosts any of the information. Why should a social application own user generated content at all. I am developing a personal knowledge store (called ArtificialMemory at http://www.artificialmemory.net) which is aiming at tackling this problem in a broader sense.