Brian,
I think that, for the large part, the rotor fracture symptom of cross-drilled rotors has been alleviated. A stress fracture needs a stress concentration to be inititiated. With regard to a brake rotor, the potential for a stress concentration lies in 1)a poor quality casting or in 2)the abrupt changes in local cross-sectional areas created by drilling dozens of holes through the disc. Given that most of the high-performance drilled rotors available today are made with high-quality rotors to begin with, that solves problem #1. Additionally, nowadays, the holes are not only drilled but radiused as well, thus creating a longer 'neck' where the x-section change occurs - thus minimizing the stress concentration factor in and around the 'neck', solving problem #2.
Further, I imagine one would need to generate more heat than one is likely to do in street driving to crack even a rotor of mediocre quality, let alone the factory ATE or Brembo drilled rotors.
And yes, many exotics use drilled rotors as stock equipment. As to whether drilled or slotted is more appropriate for street use, the new 911 Turbo has front rotors that are both drilled and slotted!
I think quality, brand-name drilled rotors should be safe - my original question was whether or not they are worth the investment for a street car.
Thanks to all for an interesting discussion thus far...
-Nick