I lost about 40 pounds about 4 years ago on South Beach and kept it off for about 3 years! This past year was quite stressful and I put on about ten pounds in the spring.

Then I went on Phase 1 in July and lost about 5. Then when school started in August (I'm a teacher) I just started eating carbs all the time. Stuffed myself Thanksgiving and Christmas - but decided I had to get back on it before I go back to school on January 4th. So I started phase one on Dec 28th. The first 3 days was very rough! I didn't have a headache but felt weak - and had to remember to snack and was (and still am) very tired. So when I go back to school I will have been on it 7 days and will feel great. I probably will have lost about 5 pounds by Monday and I feel so much better. I hope I will lose ten by the end of January and then it will be really slow - but that's okay! If it is slow it will stay off easier.
I got my mother on SBD two summers ago and her cholersterol (which had always been very high) went to a normal level for the first time ever. She was able to get off the prescriptions for high cholesterol she had been taking. She lost weight also, not sure of the amount.
Like most people, I have been on many diets. This is the only one where I kept the weight for for several years. It was great! It was very easy to maintain the weight loss - which is probably more important than the losing of the weight, IMHO. Once I lost the weight I wanted to lose - I just tried to stay off desserts/sugar. For birthdays, special occassions, etc., I would treat myself but not in excess.
Another thing is I really don't weigh myself very often. I probably will several times a week in January/February but once I start getting close and my pants are fitting again I will just stop weighing myself.
Good luck!