Somewhere, Sheldon Brown wrote a good article explaining the ramifications of leverage on brakes. Basically, if you have too little, the brake gives a nice positive feel but either it won't stop well or it will after you apply a lot of force to the lever. If you have too much, the brake will feel spongy. With too much leverage, your lever might hit the handlebar before you are applying full force, and this is unacceptable.

Some of this depends on your tolerance and strength. I have long fingers and strong hands, so if I have to squeeze hard to brake fully, I don't mind. It's entirely unacceptable for people with weaker hands. I seem to adjust quickly when switching from bike to bike. All of my bikes have adequate brakes, but when people try them, sometimes they tell me my brakes don't work.