When my 18-month old ran into the family room and said "Uh Oh Color" I knew it couldn't be good. I went out into front room/dining room and saw that he had colored on 2 walls and in the stairwell with red and blue crayons.
I immediately went into the kitchen and grabbed the Magic Eraser. I wet it and went to work on the walls. Imagine my surprise when I didn't have to "scrub" but simply wipe down the walls with the Magic Eraser and the crayon stains disappeared. The walls soon looked as good as new.
I also use the Magic Eraser on our bathtub. It removes the ring around the tub in seconds. I use it on light switches, on my son's plastic toys, counter tops, etc., and I am always amazed at how well it works. I think it has been used in every room of our house.
The best thing about it is that it uses no harsh chemicals and has no odor to it. I feel safe using in my bathroom without ventilation and using it around my son.
Update On Oct 03, 2009: Now having two kids I cannot begin tell you how often I use the Magic Eraser. I find that it really cleans almost anything. It works great on all the kids' toys. I've used it on the toys, walls, floors (Pergo), tub, chairs.