I definitely nodded of while driving, but not while using AP. I was coming back from the mountains alone in the middle of the day, driving on a four lane, divided highway in my ICE car at 70 miles per hour with cruise control on. I felt a little yawny but otherwise OK. The next thing I realized was that I had slammed the left side of my car against the metal rail in the median and bounced back onto the highway. Fortunately, no one was in my way, and I managed to get the car straight and going forward down the highway. I had a goose egg on the left side of my head and an $8,000 racing stripe down the entire left side of the car but no real mechanical damage (you have to give credit to MB - they makes a tough car).
We had been discussing buying a Tesla for some time, and after the run in with the guardrail, the availability of AP actually sealed the deal for me. I really look at AP as a safety feature if you do nod off temporarily rather than something that might induce drowsiness. It is really too much fun to drive the car to get drowsy while doing so.