I've never done it, but I had a consult at a place that offers it. I was pretty gung ho about doing it until I started thinking about my hormones. My hormones are cuh-ray-zee on my BEST day-so I got a little nervous about adding extra hormones in. It's in pill form now, and it's also a super super restricted diet b/c the hcg is supposed to "reset" your metabolism, so that it doesn't go into starvation mode.
I'd first heard about it when I read a book by..dangit..the guy who does the Miracle Cures They Don't Want You to Know About type books..argh..whatever his name is, he has a Weight Loss Secrets book, and that's the secret-hcg.
My bff asked her mom about the diet-she's a Dr..and Dr said she wouldn't put her worst enemy on it for any reason, so she wasn't about to give her daughter the ok for it. That also scared me away.