LOL.
I'll quote GRM:
"Crossdrilling your rotors might look neat, but what is it really doing for you? Well, unless your car is using brake pads from the '40s and 50s, not a whole lot. Rotors were first drilled because early brake pad materials gave off gasses when heated to racing temperatures, a process known as "gassing out." ...It was an effective solution, but today's friction materials do not exhibit the some gassing out phenomenon as the early pads. Contrary to popular belief, they don't lower temperatures. (In fact, by removing weight from the rotor, they can actually cause temperatures to increase a little.) These holes create stress risers that allow the rotor to crack sooner, and make a mess of brake pads--sort of like a cheese grater rubbing against them at every stop. Want more evidence? Look at NASCAR or F1. You would think that if drilling holes in the rotor was the hot ticket, these teams would be doing it...Slotting rotors, on the other hand, might be a consideration if your sanctioning body allows for it. Cutting thin slots across the face of the rotor can actually help to clean the face of the brake pads over time, helping to reduce the glazing often found during high-speed use which can lower the coefficient of friction. While there may still be a small concern over creating stress risers in the face of the rotor, if the slots are shallow and cut properly, the trade-off appears to be worth the risk. (Have you looked at a NASCAR rotor lately?)"
Please read, mainly the entire first post if anything. Some good info.
The real deal about cross-drilled and Slotted Rotors - IWSTI.com: Subaru WRX STI Forums
After that, dig around on the websites of manufacturers of brakes and see what they have to say about drilled vs. slotted rotors. Remember, it's in their financial interest not to talk down on essentially half their products, but there comes a point where you just cannot lie. When you're done doing that, take a peek behind the wheels of a Formula 1 or Le Mans car.
Do I speak from first-hand experience as to which one is better? No. All the cars I have driven on a track competitively or in HPDEs have had conventional and/or slotted rotors so I cannot compare. Does that make my opinion moot, though? Hardly. Doing so would be along the lines of dismissing someone's opinion that an eBay electronic supercharger or "Tornado" does not provide gains simply because they haven’t tried it.
And for the record, the burden-of-proof always lies on the party making the claim of an advantageous development or idea, not the inverse. Now show me a manufacturer, racing-team, or seasoned road-racing enthusiast who has come out in favor of drilled rotors.