Short, continuous, low-content updates about the particulars of your friends' lives—Bob has the flu, Barbara can't believe what just happened on Mad Men, Sally and Ned are no longer on speaking terms—deepen your bonds with them. Writer Clive Thompson has explored this phenomenon, what social scientists call "ambient awareness." Following someone through his status updates is not unlike sitting in a room with him and semiconsciously taking note of his body language, Thompson points out. Just as you can sense his mood from the rhythm of his breathing, sighing, and swearing, you can get the broad outlines of his life from short updates, making for a deeper conversation the next time you do meet up.It's this benefit of Facebook that seems to hook people in the end: Their friendships seem to demand signing up.