As you may know, each user has a FOAF file generated automatically for them at http://www.livejournal.com/users/exampleusername/data/foaf, containing information on their interests and people they know.
As you may also know, LiveJournal's friends list is really combination of things: a list of people you trust to read your protected entries, a list of people whose entries you want to read on your friends page, a list of people you know (but don't necessarily read on your default view, or even at all), and probably other things, too.
So if you want to specify which users appear in your FOAF file, you can do so by creating a custom friends group called "FOAF-knows". If you have a group with this name, then only users in this group will appear in your FOAF file; otherwise, all the personal journals on your friends list will appear in that file.
