Whitney Hess does a good summary of sites that do this - even includes snapshots of the services like FriendFeed for folks.
For the most part, I've enjoyed seeing who I might know because of who I know.
The hard part is when you see the same face popping up and you know a connection online isn't possible for all the wrong reasons.
Hey, I'm an adult. I shouldn't care but sometimes I do agree with Geoff Dick, senior lecturer in information systems at the University of NSW, who said "Removing someone from your friend list is almost a declaration of war."
Reporter Daniel Emerson quoted Dick March 27 when writing about a British judge who made it official: Being "Facebook friends" with someone doesn't necessarily make you their friend.
"The magistrate was presiding over a harassment case in which a woman accused her former boyfriend of hounding her by sending her a "friend request" on the popular social networking site on January 21."
The ex-boyfriend, Michael Hurst, 34, was cleared of the charge after the magistrate accepted his argument that the contact was highly innocuous because being "Facebook friends" could not be defined as "friendship in the traditional sense".
"[Popular British radio DJ Chris Moyles] has 1 million Facebook friends. Do you think he knows them all intimately?" Mr Hurst said."
And keep the friend of a friend links coming ... it's a great way to meet new people.