I used to use the rear as my primary way of scrubbing some speed, as I found it a bit more convenient than grabbing the front lever. After I read Houghton's Proficient Motorcylcing, I realized I was in a bad habit. Your stopping power comes from the front wheel, and in an emergency, you'll do whatever your habit is. My habit was developing into using the rear brake, and in the emergency, that would have sent me skidding. So I've started to focus only on the front brake, so that in the emergency situation, I'll do the right thing. I sometimes tap on the rear a bit too, but I don't have much faith in the rear. I've skidded in hard stops without much pressure on the rear. I don't think that rear brake is doing much of anything. Since I don't trust myself to use both brakes in the exact right proportion, I think my best response in an emergency is just going to be to use the front properly. Whatever I can manage to get out of the rear will be bonus.