I like to play Frisbee golf with my Discraft Ultimate frisbees, and they tend to get warped and dented over the course of a few holes. This leads to wobbles in flight, reduction in accuracy, and a generally frustrating experience. Worst of all, I tend to smack a brand new Frisbee into a telephone pole within the first ten throws!
I stumbled around the Internet and found that hot water made the difference. The 4 frisbees I recovered were warped and basically un-throwable. They wobbled all over the place and they dropped out of the sky like rocks.