The simple, draft Group Membership Protocol is now implemented on LiveJournal. All LiveJournal users and communities have their friend or member lists exposed via group membership protocol.
There's also some as-yet-unspecced, experimental auto-discovery stuff on each LiveJournal user's main journal page:
<link rel="group friends made" title="LiveJournal friends" href="http://username.livejournal.com/friends" />
This is intended to provide a simple mechanism for a site to follow up an OpenID handshake with an offer to import the members of that group. It's all largely academic right now given that there are no client implementations, but I invite people to have a look at this stuff and give feedback.