What I don't see is a simple "howto" for how to make a social network provide the data that would be useful to the google aggregator. I have a guess, and was hoping that someone could confirm/correct me.

Two steps:

1) Provide a mechanism for users to add links to their profile page on other social networking sites, and display those on the user's public profile page with rel="me".

2) On that same user profile page, where links to friends are listed, include rel="friend" on those links. Very few well designed sites will list an unlimited number of friends on a single page, though, so how should we state links between a user and subsequent pages of friends?

Then, in order to take advantage of the data that has been collected:

Implement a "check for additional friends" capability that queries the SGapi to see if any additional links within your own social network can be determined.

Seems simple enough, but then we can get no benefit until users volunteer their other SN profile pages, and likewise reciprocate from those profile pages back to this one.

This all ignores the (seemingly most useful) primary key, the sgn://mboxsha1/. I have no wish to divulge a user's email address, but I could possibly be convinced to reveal this sha1 encrypted piece of information. Shouldn't there be a way to tell google the mboxsha1 for a user so that some connectivity may be determined even before the user tells us about any profile pages on other sites? Is generating a foaf file for each user/group the only way to do this? Is that also the only way to provide details for anything that isn't normally displayed as part of the user's profile page? (met relationships, for example)