I am curious as to what Scott Blazey found impressive about the BMW all wheel drive system in this weeks Roundel Weekly. When I tried out the BMW X5 3 or 4 years ago at the BMW center in South Carolina I chose not to purchase the vehicle. The X5 was having a terribly hard time getting up and over a rock. The instructor gave lots of direction on how to go slow and let the vehicle climb up over the rock, but it just didn't want to do it. It would get almost to the top, then slide back down. The problem seemed to be in the way BMW (and perhaps other manufacturers) have designed these all wheel drive systems. I asked the instructor why I was smelling brake burn. He then explained that the way the system works is that it applies the brake onto the wheel that was slipping pushing power to the other wheel. What happened to the good 'ol locking and/or limited slip differential? My old Land Cruiser had three differentials (front, center, rear) and I could set it to lock any one of them ... that vehicle would have climbed over that rock without a thought. I understand other vehicles have either a locking or limited slip in the front, back and middle (Range Rover?). Why does BMW not use this kind of system? It would certainly save the brakes!