We just completed a road trip from Portland (OR) to San Francisco and back. The trip went great, but I have a few comments on and issues with auto-steer.
My primary issue was with changing lanes will A-S is engaged. On certain parts of the highway, in particular the 505, the lane change would either not activate (I waited sometimes 20 seconds before I gave up and took the car out of A-S to change lanes) or it would take a highly variable amount of time to begin changing lanes. This did not seem to be a function of traffic, since sometimes lane change refused to work even when there were no vehicles behind me. The condition of the road did not seem to matter since sometimes lane changed worked on poorly striped roads and sometimes it didn't work of well striped roads. I only single out the 505 because lane change consistently didn't work coming or going. I could not detect rhyme or reason for its behavior.
For the most part I really liked A-S, but I didn't find it much less stressful than manual driving. A couple of times A-S disappeared (the icon went away completely) for no good reason that I could tell. Also, short stretches of repaired road that lacked striping caused problems, especially if the repair occurred going around a curve near a bridge. On generally straight stretches of road with gentle curves it worked great. But passing semis can be more excitement than generally one needs since A-S centers the car in the lane, but if the semi drifts toward the car, one has to take manual control. So sometimes less stressful, sometimes more.
I agree with other comments here that there needs to be some delay in the activation of the lane change. And the start or lane change should be dependent on a free space in both the forward and rearward directions. I activated lane change a bit early one time and wound up within two feet of a pickup in from on me. Scared the bejeezus out of both of us.