Big Data -- the accumulation of massive amounts of information just for its own sake -- is the revenge of the nerds, a booming generator of money and power. New kinds of faster, cheaper hardware and software are providing a level of data never imagined before, including facts about human behavior. If that means more efficient sales of products to people want them, does it also mean identify theft and credit card fraud? If consumers are worried, why do they pour their personal data into Facebook and Twitter? What are the broader applications of Big Data?