I really like Orange’s Friend-O-Meter site built to promote the Motorola Dext. Based on the simple premise of “how good a friend are you?”, it can log into your Facebook, Twitter and MySpace accounts and then quiz you on your friends.
I managed a respectable 7/10 although it did remind me of the need to cull some of those lesser friends on Facebook! After the quiz, you can then post your score to Facebook or Twitter which then helps the game move on virally.
This is definitely one of the better uses of Facebook Connect I have seen recently.