ABSTRACT
Today, what can be easier than tweeting a sentence or two? With a few keystrokes, one can show and tell the whole world what he or she is up to. On Facebook, adding pictures and a short note takes just seconds. With more than 800 million users and 130 friends per user on average [56],* messages ripple through billions of virtual channels, reaching people through web, email, and mobile applications. Facebook and other social networking companies now work relentlessly to speed up the pace of interaction. For example, early trials show that a simple increase in the number of bookmarks on the top of your page from four to six leads to a 20 percent increase in referrals from the bookmarks to games. More interactions means greater profits, either through ad insertion or increased spending of virtual currencies. Liberated by the technology, information pours in [57].
