I've used it and it is great. Scupty is like clay, until you bake it (at low temperatures). When baked, it hardens permanently. It can be sanded and painted. You can also buy it in many different colors.
Sculpey (often misspelled as Sculpy) is the brand name for a type of polymer clay that can be molded and put into a conventional oven to harden, as opposed to typical modeling clays, which require a much hotter oven, such as a kiln. Until it is baked, Sculpey has a consistency somewhat like Plasticine. It is sold in many colors, though it can also be painted once fired. It has become popular with modeling artists. It is also sometimes used for claymation.<1>
Sculpey closely resembles Fimo, another brand of polymer clay. Sculpey is a less rigid composition which better suits modeling, while Fimo is better suited for twisting into cane and bead making because the colors do not blend together as readily. The plasticity is controlled by the amount of oil suspending the polymers in the "clay". Sculpey is also usually less expensive than Fimo.
http://en.wikipedia.org/wiki/Sculpey