I started using ours when she was 2 weeks old. My DD enjoys the white noise (I think, anyway) and she sjust started looking at the projections on ceiling.
We had a sound machine in ds's room already and got this because he loved to look at the fan so much we thought he might like the projection. He does. I put it on a timer when we use it so he's not looking at it forever though.
Re: what age for baby crack machine?