The IRL Social Graph
thegongshow.tumblr.com
thegongshow.tumblr.com
The Fridge is a YC company from the most recent batch (the YC demo day is today and tomorrow) that is taking a shot at this from essentially the standpoint Paul Adams outlined. It's got to be very, very tough to build something like this directly from a cold start, though. Especially in 2010 versus 2006.
If the incumbents can't do it, and it's hard to break into, perhaps the problem is at least temporarily intractable. In that case, it leaves the door open to something like Hunch's interest graph, where common clusters of interests (rather than IRL relationships) drive the connections.
[I also posted this comment to the blog post]