Things took a strange turn in the Phillips household last year when David, a civil engineer at the University of California at Davis, turned to his schoolteacher wife Cindy and said with disquieting urgency, "I'm going to go to the bank and get some money. We have to buy as much pudding as we possibly can."
Phillips had stumbled upon one of those frequent-flyer promotions in which airlines team with credit-card companies and other partners. The deal, since withdrawn, was this: buy 10 Healthy Choice products and get 500 miles--or 1,000 miles for purchases made before June 1999. Phillips tossed soup...