500 million Facebook denizens are plotting their social graphs. 145 million Twitter users Tweet and ReTweet. 3 million people are checking-in on FourSquare. Brands are flocking to social networks, some with strategies and others simply experimenting with community building. What’s clear is that the 3F’s (friends, fans, and followers) are not created equal. Those brands who examine the composition of their existing community will find that many are simply seeking access to exclusive specials and content. According to a recent…