I did the diet for a few weeks and lost about 4 lbs but I did cheat and once I cheated I blew it.
It is actually a good diet if you can cut most carbs out of your diet. It is a bit similar to Atkins because it is a low carb diet and you are allowed a few healthy carbs the first 2 weeks however after that you can gradually work fruit and "GOOD" carbs back into your diet.
I may get flamed by the ATKINs' dieters for saying this but I believe it is a much HEALTHIER diet than ATKINS because it allows you to eat healthy carbs. Totally discourages refined sugared type of carbs, etc. It doesn't promote high cholesterol proteins like ATKINs does. (not to mention the tons of chemicals found in those low carb bars).
The South Beach book has a list of what you can eat the first 2 weeks and what to avoid, and then what you can eat the 3rd week and what to avoid, and so on. There are recipes also that are good.
Basically the South Beach diet is a low carb diet but not nearly as strict as ATKIN's - it stresses healthy carbs which ATKINs still discourages (no fruit, will never get that with ATKINs). South Beach allows fruit after the first 2 weeks.
For me personally, low carb diets are not good, if I overeat my carbs on a particular day after keeping to a low carb diet for several days I get sick (faint feeling, low blood sugar, quezy, etc), so it's not good for me. I do try to "control" the amount of refined sugary carbs I eat.
If you eliminate most carbs from your diet you will lose weight but you better make a life long committment to it because if you start eating carbs you will not only gain the weight you lost but you'll gain more on top of it (i've seen this happen to many friends of mine who did Atkins)...South Beach is a little more doable since it allows carbs in moderation but it is still a committment.