There has been a lot of chatter here on Fitday about HCG. Most of it that I have read was from people who were just starting it and losing an incredible amount of weight. There haven't been a lot about those that used it and have been able to keep it off.
Anyone will lose weight if they go on a 500-calorie per day diet. I don't think there have been any scientific studies that show those using HCG lose more than those who don't.