First is whether or not the holes were cast into the rotor when it was made or drilled after the fact. Check the finish on the inside of the holes, if it's a smooth machined finish it's likely they were drilled rather than cast. The difference being it seems like cast holes have fewer cracking issues. This is kind of moot in the face of item two which is if you're not really working the brakes quite hard quite often it's unlikely to make a difference and you'll probably get as much life out of cross drilled rotors as you would anything else. Item three is the fact that race teams have long considered rotors to be consumables and that level of performance is now easily purchasable for street cars. So if you are working your brakes that hard that often then the rotors are going to need to be replaced more often accordingly.
