After driving Model 3 for a couple of years, I have to say that the touch screen is not a usability problem. The controls I need to have quick access to are not on the touch screen, and the ones that are on that screen, are controls I would have to take my eyes of the road and look for anyway.
I will have to grant that they have gone a bit overboard with putting controls in the touch interface, and I still don't get why the glove box opening button is in the touch UI, but that isn't a problem by any means.
I was a bit skeptical of the Model 3 UI, before I got it. But for me it is clearly a step up in usability from the "a million little buttons with weird symbols that who knows does what", and while that view of traditional car interfaces might be a bit unfair. So is all the "any touch screen UI in a car is bad", sentiment going around. Touch interfaces can work well in a car, as long as you don't need to use it for the drive task, but only for auxiliary tasks that don't need, and shouldn't be split seconds tasks.