looked interesting...

[http://www.outformations.com/~dek]

LOAF - Distributed Social Networking Over Email
http://slashdot.org/article.pl?sid=04/08/17/1954211

    FamousLongAgo writes "LOAF (List Of All Friends) is an extension to
    email that lets you send out address book data without compromising
    your privacy. LOAF appends a hash-like data structure to each outgoing
    email, and collects similar attachments from the people who write to
    you. These files can be queried to see if they contain a given email
    address, but they can't be reverse-engineered to reveal the list of
    addresses used to construct them. LOAF lets you check whether someone
    emailing you for the first time is a complete stranger, or appears in
    the address books of some of your trusted correspondents. And as a
    decentralized application, LOAF offers an interesting alternative to
    current social networking sites like Orkut or Friendster." 

Dale Kiefling
Outformations, Inc.
415 699-0421