Hacker/social scientist danah boyd has published some amazing research on Friendster, work that is generalizable to most articulated social networking services. Danah's research has turned up all kinds of fascinating and useful truths about social networking services, and now she's grouped all her papers together with summaries in one place: great reading.
Friendster and Publicly Articulated Social Networks by danah boyd – a 2004 short CHI paper staking out what Friendster is.
Abstract: This paper presents ethnographic fieldwork on Friendster, an online dating site utilizing social networks to encourage friend-of-friend connections. I discuss how Friendster applies social theory, how users react to the site, and the tensions that emerge between creator and users when the latter fails to conform to the expectations of the former. By offering this ethnographic piece as an example, I suggest how the HCI community should consider the co-evolution of the social community and the underlying technology.
