Great conversation so far; I've kind of avoided throwing my 2 cents in because this subject usually ends up like oil brand wars.
HOWEVER.....
Drilled is absolutely, without doubt, at this point - useless, other than marketing. It is literally the perception of performance. In the "old days" racing pad compounds did emit a lot of gas and possibly needed the holes. Modern pads do not.
In reality, drilled rotors can decrease performance, but probably only a negligible amount. A brake rotor's job, oversimplified, is a heat sink. It converts kinetic energy into heat energy. The quicker it can absorb, then dissipate, that heat, the better. A drilled rotor has less mass to do this job with. Could you tell the difference? Probably not..
Slots, on the other hand, can be beneficial. They help prevent pad material buildup on heavy braking, which results in "hot spots" that most people mistake as "warped rotors."
A great example are the SRT cars with the Brembo brakes. The first SRT8's had smooth rotors. There were "warping" issues (pad material buildup) that Brembo rectified with slotted rotors. Mopar TSB'd them at their expense. Later when the Hellcat hit the scene with 15.4" 2-piece front rotors ($$$) those were slotted, as well. The newest Hellcat brakes have less slots than the prior version, but are still slotted. Brembo isn't doing this for marketing purposes.
Do note none of those (OEM) Brembo SRT parts are drilled..
Richard