i'm kinda the same way. I've found reference markers for a lot of turns, although I don't usually remember them until my pace lap :-), but i adjust around them every lap, depeding on previous laps, how the car feels, etc.
Andy, in the instances that you do get on the brakes too early (NOT too hard, since you should be at full braking nearly the entire time after ramping up progressively) it is critical that you learn from it and tell yourself to brake earlier. However at that particular moment, it allows you to get on the gas earlier which should give you a higher exit speed. Also consider you may be over-slowing the car. Hell, you might even find that you like being able to get on the gas earlier, since it can often help to stabilize a car as well.
Another thing worth mentioning...
At my 3-day SB school at Laguna Seca, the Formula Dodge cars were not equipped with wings. This was disconcerting, to say the least, especially on the front straight, where the car felt very light and unstable. Even without wings, however, Grant and all the other instructors pounded it into our heads that we should go from gas to brake extremely fast and extremely hard. It worked, too.
Edit: Granted, they are still light cars with stiff spring rates, but hopefully you see where I'm going with this. I do realize that some people race their daily driver, so those guys will have to modify the technique accordingly.
I am no pro, but I read about what pros do and one mentioned that on the track the best braking technique is a quick jab on the brakes followed by a gradual release of the brake pedal. Not very gradual, but, I think you know what I mean. Look at any Best Motoring video and you would know what I mean...production car or race car. The idea is to throw the weight to the front tires so they can get more grip upon entry into a corner. I think this last part was mentioned before, so sorry if it was.