It seems like everyone has a loyalty program these days. Buy a cup of coffee, and you get a punch card that promises a free cup after you purchase some number of additional cups. Shop at the grocery store, and you get points to reduce the price of gas. Our wallets bulge with partially punched cards, and our keyrings are stuffed with plastic bar code tags, all in the name of loyalty. (And, of course, you have to add the original loyalty programs – airline frequent flyer clubs and credit card reward programs.) Do these actually work?