I've been on Lighter Life Lite programme for almost 6 weeks and have lost about 20lb so far. Two women I know both lost about 8 stone last year on the LL Total programme (which you follow if you have a BMI of 30+) and have kept it off.
The Lite programme allows you one low-carb meal per day (veg + protein) plus a small amount of dairy and fats, as well as 3 meal substitutes, aiming for a daily calorie intake of 800-1200 depending on how strict you want to be.
The speedy weight-loss is brilliant. The programme is expensive however, a minimum of £54 per week. I have been suffering with digestive problems though, very bad constipation, and I've now got piles as a result. I have to take psyllium husk or Fybogel before meals which is making me horrendously flatulent. Sorry if TMI - but I do feel this is a side effect which is completely dismissed by the counsellors. It is making my work and social life very difficult - have to keep running off to the loo all the time to let out thunderous great farts 
and the trapped wind can get very uncomfortable.
I'm going to stick with it for a few more weeks however until I've got down to a healthy BMI (another 12lb.)I really need to lose this weight for heath reasons - I have problems which affect my mobility (the main reason I have gained so much weight recently) and weight loss is one of the few things that will help me. I'm willing to put up with the short-term fartiness for long-term improvement to my health.
As an aside though, I do get very irritated by people assuming that VLCD diets are automatically useless and you will always regain the weight. You have to get your GP's approval to join the LL Total programme - you won't be accepted if your doctor won't sign the forms. You also spend an hour each week in group counselling sessions, to help you understand why you have become overweight.
If you have health probs that mean you are very sedentary, these diets may be the only way to shift the weight in the short-to-medium term. It can take a very long time to lose weight by more conventional methods isuch as low-carbing, calorie-counting, WW, SW etc you can't exercise at all. If being very overweight is badly affecting your health then sometimes you just have to shift it fast, then concentrate on maintaining the weight loss through healthier eating afterwards.