Another important dot-com lesson was that advertising, no matter how clever, cannot save you. Take online pet-supply store Pets.com. Its talking sock puppet mascot became so popular that it appeared in a multimillion-dollar Super Bowl commercial and as a balloon in the Macy's Thanksgiving Day Parade. But as cute--or possibly annoying--as the sock puppet was, Pets.com was never able to give pet owners a compelling reason to buy supplies online....