Most of the weight is water. I can gain or lose 5 pounds in a day, depending on my water intake, time of month, etc.

I've gone off twice - gained about 5 pounds the first week (I'm guessing it was all water) and maybe a pound a week thereafter. I eat like a pig when I'm off Atkins, though, so I'm always suprised it's only a pound or so a week.

Be sure to pick a weight-loss plan that you think you can live with FOREVER. I can't do the low fat or low cal thing at all. Since in maintenance we can have quite a few carbs, I think I'll be able to stick with this forever. Any weight-loss regimen needs a lifetime of maintenance, unfortunately!