It works all the time for some women (breastfeeding = weight loss, I mean), never for some women, and sometimes for others. Worked for me for the first one, but not for the second two. But I was/am tandem nursing since #2 was born. It's kinda frustrating, but nursing's so much more important to me. For me, it's a 3 year commitment (in an ideal world; I don't think Linda's gonna wean when she hits 3), so I'm kind of adjusting to things going a lot more slowly than I'd like.
I have found what works for me is adding more exercise. Moreso than eating less, I mean. I feel better about it too; I know that even if I don't see a drop on the scale, as long as I'm exercising I'm getting healthier. Not always enough to get me moving, but often enough.