As someone who joined a fraternity in college, there's really nothing more to it than that: close group of friends with a common interest. In my fraternity's case, it was chasing women and drinking excessive amounts of booze. In our case, it was programming, intelligent conversations, and Battle.net (to balance out the intelligent conversation). But judging by our meet-up this summer, we're all still pretty close friends. Which is awesome. Couldn't ask for more!
