Anyone who has ever used an instant-messaging program has seen the basic idea of presence. That little status bar that says "available," "away," "out to lunch" or "cursing the Mets" is your presence--the computer's understanding of how and under what means you are available.
Today, that information is stored on the computer, but is mostly acted on by other people. Perhaps you see that someone's status is busy, so you send them an e-mail asking them to call rather than pestering them with an IM. Or, you see that someone … Read more