There are several articles relevant to this discussion:
GXC:
http://media.www.buchtelite.com/media/storage/paper1203/news/2008/04/17/News/Prepare.For.Invasion-3330728.shtml
http://maroon.uchicago.edu/online_edition/article/10130

WOW:
http://www.warcraftsocial.com/
http://us.blizzard.com/support/article.xml?articleId=20588

The two articles about Go Cross Campus (from now on referred to as GXC) discuss how the game is multi-player online game about using real world social networks. The game itself is described as Risk-like where all the players control a few armies, and the commanders (elected by the teams) tell the players where to place their armies, and whom to attack. The game itself takes just a few minutes a day to play, but strategizing, recruiting, spying, and catching spies can eat up hours a day. The game is played online, but won through real life social networks.

GXC isn’t the only game that benefits from social networks. Professional online games also have strong social aspects. Very often initially joining a game is the result of friends wanting more people they know to play with. Blizzard, maker of World of Warcraft (from now on referred to as WoW), recognizes this phenomenon and actually rewards players for recruiting friends into the game (the recruit a friend program). Besides physical world friends playing with each other, WoW also creates an online social network, and in fact there is a social networking site dedicated just to WoW: Warcraft Social Network. So WoW is creating new network connections between people (or at least their in game personas).

What these two games have in common is their reliance on the social network. In both games friends recruit their friends to play. The more friends playing, the more benefit one gets from the games. In GXC, assuming your friends are on the same team as you, your team is more likely to win (the team that wins is usually the team that recruits the most people). In WoW, more friends playing means more people to play with, whether that’s trading, questing, PvP, or going on raids together. So there are very strong network effects (you get some pay off for each friend playing) in these games, which encourage spread through the network. Also in both of these games, once you start playing, you tend to form connections with others in the game, thereby strengthening your commitment to the game (in WoW this is important because to play you need to pay $15 a month).

These games, like other online games have very strong resemblance to the Diffusion of Innovations discussed in chapter 16 of the book. Once enough of your friends start playing them, it becomes more likely you will, and thereby spread the game further. Like many other products, the success of online games seems to be tied to their spread through the social network.