I've been seeing a lot of elastic thread around, but its usually on the top of a shirt or dress. I decided to try it out on the bottom of a shirt I made for my daughter, and I'm pretty happy with how it turned out. I think I'll make the shirt a little longer next time since it tends to scoot way up her tummy.
I have a Brother machine, and I've heard that they are finicky with elastic thread. Mine does an okay job, but I've found that I have to wind the elastic tightly on the bobbin to get it to work. I use it immediately, because if it stays on the bobbin that tight for too long, it loses its elasticity.