MTB: Yes and no.
When cruising or climbing or just bumbling over XC terrsain I'm on the bar ends... so it takes a little longer.
When descending at speed and swathed in the cold sweat of terror, my fingers are over the levers so I'm always only a billionth of a second from the loving security of a high-speed endo.
Road Bike: I ride on the hoods almost all the time and usually bend my elbows to tuck in rather than using the drops. That usually puts the brake and gearchange levers just where I want them.
Fixed road bike: It doesn't stop; I can't control it; the brakes are poor; wherever I have my hands I'm going to die anyway. AAAAARGH!!
But essentially, I can usually get to the brakes about as quickly on a bicycle as I can in a car.
The top, top location of brakes is on a motorcycle: Grabbing some brake automatically makes you shut the throttle. Someone clever came up with that one. I wish my fixed-gear bike had something like that...
