I haven't used them on the car, but they are amazing in the house. I had a drop ceiling put in and the installer put dirty handprints everywhere. The magic eraser wiped them right off.
I've used them on the rims, and they work great. I've even used them on the leather seats, and it was amazing the grime that came off - I didn't even realize they were dirty! I made sure to condition the seats after though to replace the moisture that the erasers pulled out.