Why People Join Social Networks

Zooming around google I came across Why People Join Online Social Networks. It offers a slightly more detailed list of reasons as to why someone might go and join a social network than our in class slides [slide 5] did. It seems nobody bothered to expand his list after it was posted but, off the top of my head, I think I can add one: to play a game. Aside from the variety of Massively Multiplayer Online Games there are plenty of websites like Newgrounds.com that allow users to come together and play simple games.