Supermarket "savings" cards.

"Loyalty" cards, "frequent shopper" cards, whatever. I've got a pocket (and a key ring) full of them. Nice long article about the concept, describing their legitimate uses and reasonable concerns, and even some of the unreasonable concerns.

I don't really care that Kroger is keeping track of what I buy, or even that they're making assumptions about my life as a result (even if they're wrong, and decide not to eat meat loaf at my house after seeing how I often buy packages of ground turkey and cans of cat food at the same time). I'm more concerned (a) that they'll take their information about me and sell it and my contact information to other companies who will then spam me unmercifully, and (b) that these loyalty card "discounts" often don't seem to be real savings at all, but are just reducing inflated prices to their normal level.

Another concern I have with these programs is that even when they use their collected information the way they intend to, and their data mining leads them to give me "targeted" coupons, they can end up with unintended consequences. When I was in Durham, the nearby Harris Teeter kept spitting out targeted cat food coupons for me with the receipt, when their data mining made them realize that I had stopped buying cat food from them six months earlier. Of course, I didn't stop buying cat food because I'd found a cheaper source - I stopped because my 18-year-old cat passed away six months earlier. All these targeted coupons did was remind me that I no longer enjoyed the pitter-patter (well, "thump-thump") of little paws around the house, and for a while, I shopped elsewhere just to avoid those reminders. Probably not what they really intended.