"It becomes an extension of my mind, an extension of my taste, my sensibility, my active memory," says Sherry Turkle, a philosopher at the Massachusetts Institute of Technology in Boston. We no longer need to remember, yet nor can we ever truly forget, because everything's out there, logged and stored. It's not so much that knowledge is power. Dominating the market in the tools people use to navigate that knowledge - which is what Gates wants to do now - is the true source of power. Own that, and is it too much of an overstatement to say that you own a little piece of people's brains?