I make a living buying and selling used books. I browse the racks of thrift stores and library book sales using an electronic bar-code scanner. I push the button, a red laser hops about, and an LCD screen lights up with the resale values. It feels like being God in his own tiny recreational casino; my judgments are sure and simple, and I always win because I have foreknowledge of all bad bets. The software I use tells me the going price, on Amazon Marketplace, of the title I just scanned, along with the all-important sales rank, so I know the book's prospects immediately. I turn a profit every time.
Sometimes the guy spends eighty hours a week in used book stores, and if you are an author think of this as your competition. For the pointer I thank Andy Howard and the full story is here.
Along related lines, Adam Ozimek thinks that "Brain Mounted Computers are a Dominant Strategy Equilibrium."