This little app really impressed me today: http://friendthing.trigse.cx/
It's basically a mapper that lays out your FaceBook friends in a "who is related to who" way. So you get clusters of people who are all freinds together - and so on.
I saw an early version of it that was just pants - but this is a lot better. For starters it listed my brother (the closest relatvie I have on there as a friend) in the middle of my "friendship map". And it correctly clustered my other friends into groups.
Ok so it's pretty useless in the long term but it is interesting to see how my friends lay out (and suprisingly how there is actually only 3 main groups of people!!). Worth a pop :D