i'll chime in (no tremendous weight loss, but hit me back in two months!)
i did optifast years ago, it worked really well for me (i think its about 500 cal a day?). i hated the cost and the taste. on my own, i use one tblspn carnation instant breakfast mixed with 8 oz soy milk (cheaper than slim fast and virtually the same ingredients). i start at 11 am or noon, drink one every 2-3 hours, stopping at 6 a day. i drink all the water i want. this works out to 990 calories a day.
nowhere near as hardcore as the other fasters in this forum, but i think we can all agree, we do what works for us. my drinks really help me out b/c it's constant feeding, i like chocolate... it'll take longer than my fellow fasters, but i know that under 1000 calories a day will eventually lead to weight loss. best for me to do it a little slower with long term results that doing it rapidly and then bingeing.