"The woman next to you on the bus, typing madly on her laptop, just might determine the ending to next year's blockbuster film or how quickly the hottest new PDA hits store shelves. In homes, dorm rooms, coffee houses, and waiting rooms around the world, millions of people are exercising enormous influence on what we buy - even though they have no official connection to those products and services. Who are they? What motivates them? Marketing experts...