I've got a Ford Fusion with the lane keeping system, and sometimes it will act up, for instance if there has been construction and they've redone the lane lines, the system somehow picks up the old lines and tries to keep me in them. Or on rare occasions when I have to swerve around something on the road, it fights back. But as long as you've got both hands on the wheel, you'll win against the auto-steering with very little effort. Even one-handed, you just have to be a little assertive with it. "No, you're not steering me off the road today!"
The system is a bit strange to get used to (not nearly as strange as adaptive cruise), but overall it's pretty well implemented.
They also have it set up so if the car thinks you're not holding on to the wheel, it pops up a warning message over your dash screen to keep your hands on the wheel. They have this to make sure you're holding on in case it tries to go somewhere wrong.