I’m fascinated by social network theory. It’s fun to map the relationships of individual actors within a broader social web.
While most of us may think of network theory in the context of internet social networks and our own relationship-building efforts (weak ties vs. strong ties, etc), I fondly recall a moment in my high school psychology class where I insanely suggested we map out the cliques in the senior class. A couple minutes later the black girl in the class (who volunteered information about the "minority group") was going at it with the "beautiful blond," one other girl was close to tears, the jocks were all laughing, and soon enough the teacher ended the ill-fated exercise. Ah, high school, our first exposure to social networks, connectors, and orphans.
Anyway, if you want to get an academic introduction to social network theory, check out this free online textbook by a UC Riverside professor. I recommend reading the first chapter to get an overview of how the field operates.
(Hat tip: del.icio.us/chrisyeh)