Just to keep adding to the knowledge - from all the research I've done, if you want to get drilled rotors look for two things as indicators of good quality.
First, it is critical that the holes are chamfered (beveled). This reduced the stress riser effect and will help to mitigate cracking. It's also a good indicator that more thought and effort has gone in to it than simply "Me make hole."
Second, it is preferable that the drilling is done by the manufacturer of the rotor. This ensures that the rotor was originally designed to be drilled one and has the appropiate structural and metalurgical properties.