I missed out on this thread, since I was off galavanting from place to place.
I've finally started doing weighted chins - either 4 sets of 5 or 3 sets of 6 with 10 lbs. I do them with two hand grips - under and hammer. I haven't done over, wide grips in a little while, but was doing sets of 6 when I did them consistently. Now I'm working on bumping up the weight. I'm eyeballing that 45 lb. plate...
That's the whole key - you have to do them consistently. At least once a week, or better yet, start every lift with one set to failure. That's how I developed my initial chinning strength.