I'm new Tesla S85 late 2014 owner with AP1.
I made two road trips, 400km each, mostly on side roads and i used AP 70% of the time to test it and to know it limitations.
I've read for months, posts from other real life tesla users, to be sure what to expect, but finaly AP1 was above my excpectations.
I thought that AP in it's current state will be useless on side roads, but it's quite good if you know what to expect and use it as driving help, not to drive for you.
Of course you can use it only where lines are clearly visible, but even on roads without emergency lane.
I was suprised how well AP1 keeps in middle of the lane and how well it handles curves, while driving on polish country roads at 90-100km/h.
During this 800km trip i had three situations which would be dangerous if AP1 was left unattended.
First was on traffic island which was not correctly marked with road lanes, which AP passed turning wheel abruptly right and i was affraid that it'll hit curb, which it probably wouldn't, because it started to turn left as i took control, but i didnt want to risk wheel damage
Second was up hill when road was turning left and at hill top curve changed to right. There was no traffic at oposite lane so i left AP on and it crossed middle line around 1m and got back to previous lane after which AP shut off.
Third was most dangerous if it was uninspected. There was sharp curve with lines and suddenly all lines dissapeared leaving all road black blending with dirt on side road and AP started to drive straight which would finish in forrest if i wouldnt take control.
All above sytuations were clearly visible to me long before they happened and AP was left on intentionaly to see how it will react.
For now it is more than i have hoped for. It will not drive for you, but it's driver assistance, which will let you take off eyes from road for few seconds to do something.
I'm driving twice a month 1500km trips mainly on highways, so i concidered only Tesla with AP, because trips are so long and boring. To be honest behind the wheel when traffic is light on highways i sometimes browse through emails, messeges etc to ease the trip. Switching eyes from windshield to phone screen for few seconds. Yes i know - it's dengerous and forbidden by law. Many of us do it, rarely anybody admits it. Thats why i needed AP, to do what i did with regular car (without TACC) for past few years, but safer.