While it is possible to warp a piece of cast iron, it is not easy to accomplish. this white paper on the stoptech site shows that there are other faults that might cause the tremolo you feel in the brakes.
I had my rear rotors turned when they were warped. They were straight for a couple of weeks, then the warpage returned. Just replaced them last weekend. I think the warpage may have been caused by the parking brake not releasing fully.
Haven't rec'd my FSM yet, hence the easy questons. Is the parking brake drum attached to the rear disc? So it's basically a tradition parking brake arrangement attached to a normal disc brake system? My subarus are this way.
I definitely need to check out the parking brake when I swap the rotors. In response to Dan, I need to check the tolerances. I have a set of pads, complements of Dan, but did not change them when I had the fronts done.
Are the rears easy on full floater or is dismantling of the hub involved?
The rear rotors are held on by lug nut pressure alone - no hub dismantling. Remove the wheels, and with a little jiggling the rear rotors and integrated rear drums come off in about a minute. For persuasion, there's the threaded hole in the drum to push them off while tapping with a hammer every thread turn.
I did the rears in about 2 hours including putting the tools away. Fronts obviously require wheel bearings.
Get familiar with the parking brake via the FSM if you're planning to adjust them as it's said to be tricky. Mine were a piece of cake, so I must have gotten lucky when I adjusted mine. The brake shoes were almost new looking.