Mouth publishing is the best way to advertise something. It affects more than a TV advertisement. Social networking is spreading worldwide like an epidemic. Whatever people do, they share everything over the net. They even write about what they are currently doing, what they are feeling and what are their plans.
If you collects and analyze all data correctly then you can predict about what most of the people are about to do. You can know the people habits of particular region, or their need or current trend, fashion and many things.