[rdfweb-dev] Plink – plink.org is going down due to the inability for FOAF to be expired. Lack of control of proliferation of personal information is one of the major hurdles (a subset of the larger question of publishing control [see: Towards Semi-Permeable Blogging] and data control/faceting [see: Capabilities Theory]) in moving towards larger (hopefully open) identity management and relationship management systems.
Certainly, one way to do it is along the lines of using PKI and encryption to create classes of data encrypted on per-user, per-group bases. Keys could then be directly managed and revoked to limit continued availability within the system regardless of the distribution of the encrypted data (spread it over Freenet or other P2P for caching!). There are also other ways of expiring data, but those should remain in confidence for now.