I don't know of too many surfaces that it doesn't work on. Like Dan said, you have to keep it wet and you don't have to rub hard either.
Frank with a name like Effie she should be driving a 53 to 56 ford truck. I sell wizard products on the side (so does MavMark) I think it is the best stuff going (my ) been using their clay for awhile. The Shine Master, which is a no-wax no-silocone breathable sealant is awesome. If you have a chance to try it out I think you will be suprised, with any of their products for that matter.
Do you think it would work on wiper blade scratches? I would love to find an alternative to the messy drill mounted polishing compound stuff from JCW.