This is interesting -- a researcher at the University of Wisconsin-Madison (just up the road from me here in Chicago) says that World of Warcraft is an emerging new "third place." That is, it's a place in between your work and home where you make friends and otherwise interact with new people. Starbucks has even used the term in their actual marketing (to try to make their coffee shops a hangout more than just a place that you stop by and grab a cuppa joe), and WoW isn't even the first videogame to fit the critera -- Sony advertised the Playstation 2 as a "third place" in Europe.
But even though Blizzard has never actually marketed the game as a "third place," it almost fits the definition most. Sure, it's not actually a different place -- most people do play at home, I'd imagine -- but in terms of having a different crowd of people that you interact with outside your home or work, that is often exactly what WoW is for us. As Professor Constance Steinkuehler (who has a pretty wild website for a college professor) says, "most people go for the game and stay for the people."