I agree with SkinnyLegs. It's the people not paying attention that I worry about. My motto is: everybody stay on their own side of the white line, and I'm happy.

Lightly traveled rural roads with no shoulders are a different situation. There, my position on the road all depends on the circumstances, though I tend to stay far right for similar reasons. I've developed the habit of glancing over my shoulder when there are only occasional cars approaching from behind--to make sure they're not in a trajectory that's going to hit me. I figure I've got time to go ditch diving if they are.