Facebook announced a new search tool today that lets you search through your "social graph". Techmeme's front page has plenty of commentary.
I wrote myself this unpublished note about it a few years ago, which looks pretty much spot-on now:
For each person in your rolodex, draw a little graph of how they are related to others. There might be a few or there might be a dozen links you'd want to make explicit, and each link would have a name so the edges of the graph are also labelled.
Then, when you want to surprise someone with a plausible association, or bring someone to mind who had been lost to mind, you shuffle the rolodex and unearth the connections that had disappeared but that because of your graph will reappear.
Of course "rolodex" will never show up in a Facebook press release, and the fact that I even mention it makes me look old.