I've lost a lot of weight in the past doing shake diets (Optifast, Kicstart are a couple I used), metabolism was terrible afterwards though so once I stopped I slowly regained the weight again. I also got a lot of headaches and not a lot of energy (which sucks when you want to exercise as well as diet).
Handy as a diet kickstarter if you have a lot to lose but honestly you are better off looking at a healthy diet if you are after long-term results. This is my 3rd time losing a huge amount of weight (38kgs lighter than July 2011 when I had my son). The difference is this time I've maintained my weight for about 8mths (in the past I'd be up and down 5-10kg constantly) and I'm no longer in the diet yoyo, I'm eating normally.
I am currently working on eating cleaner, mostly for my health. I did use shakes on occasions but they were protein shakes and usually had this after a workout for muscle repair not as a meal replacement.
In the beginning I had a food diary and calorie counted, regular meals and portion control, I didn't cut any food groups but didn't overbalance them either (eg. everything I ate in the past was death by sugar or carbs), still eating treat meals and regular exercise (stuff at home mostly, dvd workouts, exercise bike & weights).
PS. I hit a plateau when I was sticking to a 1200 calorie diet (which is more than what some of these shake diets actually contain) and the way out of the plateau was to eat more and change up my workouts so I wasn't do the exact thing day in day out and also having more rest days and treat days.