If you have a strong stomach, take a look at this article from the New York Times. It discusses how stores use the wi-fi signals from your cell phone to identify you, tie you to a large database, track what you look at in the stores, and even define if you are a repeat customer. The article is a sobering reminder of how little privacy we have and what does privacy mean in the era of big data
Does it matter if everyone knows how much money you make, how you spend it, where you go in your free time, and how to entice you to spend more money? Why should we care, after all, the retailers claim this lets them customize displays to make us happy.