When manufacturer JanSport receives one of its backpacks for repair, it sends out an offbeat response that helps cement customer relations. It's a postcard that reads something like this: "Hi! Warranty Service Camp is really cool. They say they're sending me home soon. Gotta run...we're doing zipper races today! --Little Pack." Dana Miller, manager of the company's warranty-service center in Everett, Wash., reports that most customer letters used to be negative; now 95% are thank-you notes.