Surface rust is rarely a problem, a reasonably spirited drive will quickly burn it off. If the surface of the disks are badly pitted then it can be a problem though this is rare on regularly used cars. As a general rule don't put the car away straight after washing it or you will definitely see rust the next day, a short drive to dry the disks off is always worth doing. Only thing to watch is dealers who will try to replace discs because of a little surface rusting, Porsche are notorious for this, which at 700 big ones each is a pretty pricey scam. HSE TD6 (Java Black/Ivory)
911GT3 (Guards Red, carbon interior)
ElanSE (BRG)
Panamera Turbo S
Boxster S