I have not personally tried it, but my mom has lost about 30 pounds in 4 months using Medifast. She did it to prep for my wedding, she needed something that was strict and provided a lot of accountability. Now that the wedding is over, she hasn't gone back to the center but she is taking some of the things she learned on with her. She is replacing some of their product with low-sugar, high-carb meal replacements, things like that. I think it was a little too limiting for her to stick to long-term, but it helped her to get her mind back on portion control and away from thinking about food all of the time.
I'm pretty sure there is a Medifast thread under the general diet plans section of this site. Good luck!