No clear objective on Facebook
An e-book written by C. Weng, called The Web: Hidden Games, says that improving social sites has to do with perceiving them as giant games.
The e-book is available free on Lulu.
Digg, for example, has countless players — much like a MMOG. The goal is to get your "digged" pages to the front. In order to "win," you must boost your rep in a competitive atmosphere among myriad fickle users.
The book also compares YouTube to chess: "There are an infinite number of ways to win in YouTube but it only occurs under certain conditions. Every single method, strategy, and theory leads back to the essential factor: getting people to view your videos," it reads.
As for Facebook, Weng compares it to The Sims, where the object is "to guide characters in daily life rather than win at something."