I've done two interstate road trips across Vic. and SA highways, and got to appreciate the AP very much - way more relaxed after 10 hours on the road. However, it does require a bit of overseeing at times - i.e. turning off in certain situations. As others have mentioned, it tends to hug an outside line on LH bends and when something's coming the other way (usually the case, it seemed) it's best to take over.
Sometimes approaching a LH bend, with lane lines partially hidden by a bit of rising road ahead, can make opposing traffic appear to be coming at you in the LH lane, and again the AP hesitates momentarily.
On the same country highways, but in different weather, I've noticed something interesting about the car's phantom braking occurrences. On a bright sunny day with tree shadows across the road, occasionally the car would baulk momentarily at one shadow out of a whole kilometre or more of roadside trees. Doing the same trip on a cloudy day and it didn't hesitate once, not for the same rows of trees or for anything else.
After 5000km, I've developed a sixth sense and can often predict a hiccup in our progress, moving my right foot over the accelerator to catch it.