I did. In 2010 I lost 59 pounds on Medifast. But after I went off, I found it very hard to keep it off. I could eat SO little in order to lose or maintain. I was down to 1000 calories a day and exercising and still unable to lose more. However they do have a new program now that looks more reasonable. The plan I did was called "5&1 Plan" and was just 5 Medifast meals a day plus a Lean and Green meal (meat and veggies). It was about 800-900 calories a day and my metabolism tested as very slow afterwards. The new program has more calories and carbs, I believe, and even includes fruit, so if you are doing that one it might work better for you.
You can read about my Medifast experience on my blog. Here's a link to my Day 1.
Medifast Begins