Take a look at the video (
Video: BMW X5 Adaptive Drive) on this page:
http://paultan.org/archives/2006/11/...ive-in-athens/
Its about 1/3 of the way down, watch the entire video, especially the last part. It does an excellent job of explaining the Adaptive Drive and exactly why it provides a much smother ride than the X5 w/o this feature.
Well worth the $4500 and the reason I chose the X5 over the competition...I would not buy an X5 w/o this feature.