I've steered (pardon the pun) clear of this thread as I am not a mountain biker. I am a roadie and am interested in improving my turning skills, although, I ride some of the straightest, flatest roads in America.
I do agree that we need to lean into turns, and, I've been playing with various body movements to develop more lean. What I've discovered is that using the Harbian "counter-acting" shoulder movement, that is turning my shoulders away from the direction of the turn, while remaining seated, lets me lower my inside shoulder very easily and tips my bike and body very effectively. The Harbian reference was done on purpose as ski philosophy is to develop the proper body movements to effect an outcome, which to me makes sense.
A simple test of the concept is to ride at low speed in a straight direction. Twist or pull your right shoulder backward and a little up, and, the bike will begin to turn left. Straighten out, then pull your left shoulder backward and a littleup, then the bike will begin to turn right. Using this technique going around simple 90 degree corners provides a lot of turning power and grip.
The "your mileage may vary" concept may apply to the above, but, it works for me. Again, I've almost never been on a mountain bike on terrain for which they are designed.
Thoughts?