@Feryll - I agree that the jury is still out trying to decide whether these so called slimming belts are as good as most of us hope they are. Time will tell. However, what does work for slimming down the mid section is a solid routine of crunches combined with a regular walking or running routine.
The running and walking will burn calories and the crunches will help to strengthen and tighten the stomach muscles. You can even wear the slimming belt while you are working out.