Mark Pilgrim compiles blogrolls from his referrer stats, then from the blogrolls of the people he links to in his blogroll, then one level further.

Update: Mark does it with the Google "related links" feature too, and says it would make a nice web service. It's my opinion such web services will most probably exist by next year, if not sooner.

06/04/02 update: my neighbor Mark did it rather sooner than later! Hmm, that's strange, in fact I am Mark's neighbor but he's not mine. What gives? If I understand correctly, some of these lead to me, while these don't lead to Mark.

"Unreciprocated neighborhood" is going to be one of the social phenomenons we'll want to discover and try to explain ("this guy knows someones in your community, but no one in your 'hood knows him yet, or acknowledges him.") Is it "Hello, I'm talking to you, why do you look the other way around?" or rather is it about those friends whom you hide from each other ("Hmm, I'm not sure they'd get along that well.") Maybe we're just overestimating the meaning and value of a simple hyperlink.