Here's a comparison of a new disk to one that was used to strip two fenders, a hood and a gas tank out of a '51 Chevy pickup. The worn disk would still have more life if I hadn't gummed it up with some weird paint that was on the gas tank.

LATER EDIT: I cleaned the gunk out of that disk by running it against a screwdriver and I got more use from it.

One of the best things about these disks is that, under normal circumstances, they never get dull and they don't load up. As they are consumed they simply expose fresh, sharp grinding surface.