At the Identity Commons we’re building a persistent global and/or local identity infrastructure using the OASIS standard for Extensible Resource Identifiers (XRI). Coupled with XRI Data Interchange (XDI) and the powerful link contract mechanism, we are building a system for personal profile control and interchange that rivals FOAF (though once again I have to make the disclaimer that I am no FOAF expert).
Given the tremendous popularity of FOAF, we’ll have to “embrace and extend” FOAF with XDI. The biggest problem with FOAF is that profile sharing is done on a FOAF-file level of granularity, so I’d actually have to have multiple FOAF files if I wanted to share different information with different entities. Storing all the FOAF info in a database and dynamically creating a specialized (WRT the requester) FOAF file is one way to get around this limitation. But even then, the requester now has a copy of the file unencumbered by (e.g.) XDI link contracts that could prevent him/her from passing it on or otherwise using it in manners originally unintended.