I love the Master Cleanse because no one in particular makes any money on this. No "products" to buy and no supplements to take, yet it does an effective job at elimination. (Editor Note: you do have to purchase the ingredients since most people do not keep cayenne and Grade B maple syrup on hand, not to mention what is needed for the salt water flush.)
This is a tough cleanse, and there are lots of subtleties that may get neglected without enough research and someone with experience guiding it. Rarely do I recommend this cleanse to people in my practice, because the side effects and the managing of the diet requires a lot of vigilance.
However, that being said, it work and forums like these provide a lot of the necessary information.