Humidifier

Does anyone use a humidifier(something like you'd find in walmart) in their snake room to keep the humidity in their racks up?

Specifically for ball pythons? If your using a rack system you shouldn't have any problems getting 50-60% humidity. Unless you find all your animals are coming out with stuck sheds, then its probably not neccessary. Even if you do have some stuck sheds from time to time, you may have an easier time just giving them a mist once a day or drop some damp moss into their tub during their shed cycle.
I also don't know how effective those would be at raising the humidity for a large area, but I've never used one before.