I enjoyed this article's technical depth on the communicative aspects of social networks. In school I was taught about an effect of democracy, where in the larger a community grows, the content becomes the lowest common denominator and diluted to fit the masses. Niche content absconds to areas that are less visible and become filtered out. One of the reasons a community like reddit continues to thrive is that the niche content is separated into filtered areas of distinct denominators. Moreover, it's also why big subreddits tend to fail and break off into smaller pieces.
Compuserve/the well->Prodigy->theGlobe->geocities->friendster->myspace->facebook->[fill in the blank]->