I recently visited LegacyGT forum and noticed you have been actively giving advice to members with your in depth experience and knowledge, which has received my attention and respect as it hard to find nowadays in various medias or web forums.
Since your posting generates some good discussions about drilling / slotting again just like anywhere else, I would invite all the members to view our comparison on different disc surface finishes.
The rotor cracking is caused primarily due to poor casting quality or more precisely - Microstructure, this makes the rotor more prone to deformation (warping or cracking) under heat. Thermal fatigue makes the rotor loses it's strength, not because of the drilling. Jerami1981's experience should well support my statement.
Anyone, especially racers, should be aware that a well performed rotor shall be made available from ground up i.e. good material (casting and heat treatment) which is more resistant to heat and better designs that will drain heat faster and keep the disc cool, rather than centering around "drilling" or "slotting" which although can change the performance to some extent, would not principally change the physical property that dictates how a rotor performs. See http://www.racingbrake.com/main/rotor_is_important.asp
which was in response to Mazda 3 forum discussion about aftermarket rotor. http://www.mazda3forums.com/index.php?topic=24716.0
Our rotors are built from our experience and know-how. See our patent pending designs http://www.racingbrake.com/main/technology.asp
. All designs are simple to understand and work. For example WRX enthusiasts love our rotors, while other manufacturers /suppliers including OE keep warping, why? it's is because our patent pending design of reinforced rib that makes the difference: