I went on a bit of a MMO researching kick today. Initially I was looking to spend a few hours playing a MMO, but I wound up being more interested in learning about the history of some interesting MMOs.
It turns out Star Wars Galaxies has a really interesting history; the designers were trying to create a society built around weak ties and interdependence, and chose game mechanics based on that goal.
The former lead designer wrote a series of blog posts discussing the design decisions and intent that went into the game. You can find them here. I found them quite interesting, and it got some of my creative juices going about how to set up online communities in general.