It is a MUST-have for us. We have forced hot air as our heat source...it's awful. My dd sleeps much better with it on and I've used it in her room, in the winter, since she was born. Sometimes, I'll even crack her window a bit just to get some of the moist fresh air in.
Re: Humidifiers?
We had a cool mist one in the girls room probably the first 2 years. The white noise helped, and it kept it from being super-dry in the winter.