I live in Reno, Nevada, and regularly make trips to Sacramento and San Francisco for business. So the trip over the Sierra Nevadas on I-80 is very familiar to me. In all my previous cars, I learned to virtually never use the cruise control (CC). Why? Because in the mountains, the CC in an ICE car will "hunt and lurch". I'm sure you know what I mean unless you live in Kansas or West Texas. As you start up a hill, the car looses a couple of MPH until the CC realizes that it has to step on it, but then, it downshifts and lurches forward. It is annoying at best, and at worst is probably not all that good for the transmission. And the worst thing is, there is no regulation going down hill. I once got a ticket on CC, where the CC was set to about 70 MPH, because I was going down a long down section, and the car (a Lexus RX 330) got up to 82!! Argghh!
Now, along comes my Model S. I set the CC on about 71 MPH and never think about it, unless traffic gets in the way. As the MS "feels" the ups and downs, it quietly and smoothly accelerates and, yes, decelerates (using Regen, of course!), keeping exactly 71 MPH. It doesn't matter how steep the grade, you really don't even notice that the car has changed. Zen motoring, at its best!!