There's a new joke making the rounds: "Who's having children? People who can't afford dogs." Canine-driven consumerism reached a new high of $21 billion in 1996, according to the American Pet Products Manufacturers Association. And a 1995 survey by the American Animal Hospital Association showed that 7 out of 10 pet owners think of their pets as their children. In fact, nearly every goody once reserved for pampered offspring is now available for Rover, giving new meaning to the expression "It's a dog's life."