My girlfriend did it not long ago. She said she felt really great, after the initial shock to her system of not having actual food and all of the sugars and processed crap she usually ate. Though she did say that sometimes after having the juices (particularly the veggie-only ones), she sometimes felt nauseous which is apparently common because your body isn't used to that huge hit of nutrients. But she had aimed to do it for 10 days and only made it to 5 before caving and having to eat more actual foods. She stayed eating fruit and veg, and juicing for another 5 days and then went to clean eating. She said it felt great to have all of the 'food' she needed in one drink.