Here's a neat article about finding the mastermind in a social network... who do you have to eliminate to break the whole thing up? Who's got the real power in the group?
Who’s the most important player in a group? Who’s merely peripheral? Data crunchers find out by plotting people as “nodes” on computerized graphs, forming web-like networks. The links between nodes are then weighed and analyzed using matrix algebra and other tools.
And it's not the "hubs" who know everyone, as you might suspect. Social network analysis (SNA) is an emerging part of artificial intelligence, especially as we struggle to dismantle terrorist networks, and this stuff is pretty cutting edge.