Retail coupons, those small cards or slips of paper that offer the supermarket shopper a few cents off on this product or that, have come of age. They are no longer a nickel-and-dime business. Billions of them are distributed each year by grocery-product manufacturers. Millions of dollars’ worth are redeemed, too, sometimes with tremendous impact on a manufacturer's marketing program. Here are some interesting data about coupons and what makes them so attractive to the contemporary, value-conscious shopper.