[jmillet]

I've got at least fifty heat cycles on my OE rotors and have experienced no warping or cracking. I've used both Performance Friction PF-01 and Raybestos ST-43 brake pads with good results.
Sometimes shuddering resulting from pad material buildup on the rotors is mistaken to be an indication of rotor warping. This can happen when street quality pads are overheated during heavy braking track use and the pad material is unevenly deposited onto the rotor surface.
Suggest you first clean up the rotors using Gumout carb cleaner and rough them up using a sanding block and #100 emery paper. If that doesn't work check them with a run-out gage. If they are in fact warped your 4 year/50,000 mile BMW Maintenance Program should cover replacement. Be sure you have the OE pads installed when you visit the dealer and I would refrain from mentioning the circumstances under which the warping might have occurred