Anyone who's talked to me for more than 30 seconds already knows outside of social games, my main area of interest is evolutionary psychology, the application of Darwinian evolutionary theory to understanding human social behavior.
Fortunately, there's a lot of crossover between the two fields, especially with game design. Here's the first of some insights that might be useful to you.
Humans are obsessed with social status. Higher status equals better mating opportunities for males. Mating with high status males, means more foods and resources for females. Before anyone accuses me of sexism, I'll simply state that this pattern holds true for all known human societies from ancient to modern, so don't blame me, blame human evolution.
In social networks, it's (very) roughly represented by the number of friends on has. A rough estimate, because there's no way of knowing where a person stands in relative social status to other in that group of friends.
This need was quickly met by developers and led to some of the most popular apps on Facebook. Top Friends let people knew who your top friends were, as did Entourage. Friend Wheel showed connections between friends.
Then a wave of ranking apps appeared: Who's the Hottest?, Sexy Friends, and Compare People. These apps allowed people to determine their social status in their friend group and one Facebook as a whole. Unfortunately for these apps, social status doesn't change rapidly and so there isn't much need to return to these apps once you've determined your social status.
Then, Friend Exchange games like Friends For Sale! and Owned! created an explicit connection between a numerical value and social status. These games literally told you what you were worth in relation to your friends and the Facebook community. Best yet, these values always increased so you could watch your perceived social status increase and you could bestow that status on to your friends.
The status values created by the friend exchange games were artificial, and more and more reflected the game environment rather than real life. As a social status indicator, they became less valuable, but nonetheless satisfying for validation.
At the moment, I think there's a huge opportunity for another game/app to emerge that caters to human's obsession with social status. Something that innovates on the friend exchange model and more accurately reflects offline social status. If people can compete for status in a game that gives them real social benefits in their offline community, it will mint money.
Or you can just clone Who's the Hottest? and call it The Coolest Person Contest. Oh wait, that's been done (very successfully).
On Monday, I'll talk about how games traditionally use social status, so hold your comments about leaderboards and Warcraft armor until then.