Paul,
Advice to me has been along the lines of - holes reduce disk surface

area,

reduced surface area is less brake clamping area.
George (down under)

Yes but they are widely used in road racing with great success.

Paul Lamar

Paul,
Sorry I didn't say this before but it was put to me that they are mainly for
cooling in extreme/ extended braking conditions.
I can't be sure myself, these opinions are from a disk manufacturer here
locally, that has the expertise.
Just thought I'd tell you FWIW.
George (down under)

 George,

          I've been told that slotted *and drilled* rotors are dangerous
for a street car. I've been told they can crack easy. But, what the
heck, they do look nice!   At the most (for street and for looks) I'd go
with a drilled set.    I'm swapping the stockers out for a set of
drilled rotors and Wilwood Superlite calipers. They'll look sweet with
my  Centerline RPM's .  :)

Phil

There is a lot of Porsches (Beverly Hills VWs) running around SoCal
with drilled rotors :) 

Paul Lamar
 
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