It is supposed to detox the body and provide a quick diet. It lasts 10 days with 2-3 days of transition back to solid foods.
Yea, it is called the master cleanse. Just google that or "lemonade diet" and you will get tons of links I have not tried it but afriend of my did and she said it was a challenge but rewarding in the end.
I found this blog from a guy who did the Lemonade diet and video blogged the whole 14 days.
http://www.lemonadecleanseblog.com/
Here is a woman who did it and kept a really detailed journal. A funny and interesting read.
http://yestheyrefake.net/lemonade_diet_cleanse_journal.htm
P.S. She also has a pretty interesting website: http://www.yestheyrefake.net
Here is a video with the receipe and how to make the Lemonade