Here's the blurb on a story that is in Forbes Magazine:
The Rip-Off: Reebok calls it the EasyTone; Skechers, the ShapeUp. These curved-sole shoes, transforming people into human rocking chairs, cost up to $130 and promise to keep you fit even while grocery shopping. During 2009 sales grew 14-fold to $245 million, estimates market researcher NPD. One problem: "They mostly affect the foot and ankle," says Dr. Michael Ross, director of Rothman Institute's Sports Performance Lab, which counts the Philadelphia Eagles, Phillies and Flyers among its clients. "There is no evidence they will help you tone better or quicker than a regular shoe."
How to Avoid It: Join a gym.