Actually, to make that work I think you'd need to add three things:
1. An extension to the vCard format to represent relationships (maybe this already exists? can you embed RDF triplets in vCard?)
2. A plugin for the popular mail servers that displays vCard info of its users as html in response to web requests (with appropriate RDFa metadata).
3. Some way to make an http request that proves "I am johndoe@example.com" or "I am the mail server responsible for johndoe@example.com" so that servers could make a distinction between private data, public data, and "friends only" data. Maybe have a chain of trust that starts with DNSSEC keys?
>1. An extension to the vCard format to represent relationships (maybe this already exists? can you embed RDF triplets in vCard?)
There is FOAF ("friend-of-a-friend", based on RDF). At the moment, this is mostly provided by websites (such as identi.ca), but could also be transferred via E-Mail.
There might be some way to embed FOAF into vCard, but why should be care? E-Mail allows for more than one attachment ...
Without the plugin people won't be findable in Google (which is/was one of the major drivers of adoption for Facebook). Also there'd be no way to look people up that you haven't been in contact with (a la finger).
Actually, to make that work I think you'd need to add three things:
1. An extension to the vCard format to represent relationships (maybe this already exists? can you embed RDF triplets in vCard?)
2. A plugin for the popular mail servers that displays vCard info of its users as html in response to web requests (with appropriate RDFa metadata).
3. Some way to make an http request that proves "I am johndoe@example.com" or "I am the mail server responsible for johndoe@example.com" so that servers could make a distinction between private data, public data, and "friends only" data. Maybe have a chain of trust that starts with DNSSEC keys?