And I can't help that it remind me of everybody's "favorite" screen/dial integration:
I find one of the problems with the iDrive is that the knob is horizontal, and the screen is vertical. It's difficult to "map" movement from one to the other, plus the knob is very hard to reach comfortably. Well, that and the iDrive software just isn't the best.
Contrast that to the knob in the 2005 Acura RL (about the same time as iDrive came out):
The knob and screen are on the same plane. I found this interface to be wonderful to use. The knob turns clockwise/counterclockwise with detents, and pushes "in" as expected, but it also acts as a digital joystick with 8 ways to push it along the compass rose. What isn't clear in this picture is the way the elbow rests on the arm rest, with the wrist supported by the shifter lever, leaving your fingers resting comfortably on the knob. Also, the knob had HEFT--you could give it a could spin and it would keep going for a few detent clicks. Combined with a great "arc" based user interface on the screen, and audible feedback on where the knob was "pointing" to, this provided a very nice eyes-free input device. I prefer this to the Model S's touch screen keyboard for inputing numbers and text.
Interestingly, the same really good NAV software showed up a few years later in Honda's but with a touch screen without the nice knob. It's not even close to the same experience.
I chalk it up to having something to rest my arm on while using it. In both the Honda and the Model S, to use the screen one's arm must be suspended in free space. This is fatiguing over time, and the weight of one's arm makes hitting precise touch points difficult. On the Model S they make sure the touch points are rather large which helps. But the support of my arm in the Acura made a huge difference in usability.