Originally Posted by vividracing

Contrary to popular belief, rotors RARELY warp. I've only seen it once, and I've done plenty of brake jobs. It's almost always a case of uneven pad deposits on the rotor. Hard braking will remove the pad deposits in most cases.

Take a look at this article by Stoptech that covers a few myths about brake systems, including warped rotors.
-Warped- Brake Disc and Other Myths