I would never go below 1500 cals unless you are very near your goal and weigh less than 150lbs.

Even though atkins gives you a metabolic advantage, you will eventually have to watch your calories to continue losing. I can eat around 2300 cals/day and still lose consistently. I think thats a very reasonable amount of food. However, if I stay "low carb" but eat 3000 a day, I may lose but it will be VERY slow.

At this point, I'd have to say that the main reason I stay on Atkins is to prevent muscle loss and control hunger. I couldnt hack 2000cals a day if I was getting a high percentage from carbs, I'd be hungry and probably start getting weak on the weights.