Everyone. Everyone should pass on the left; but really, it’s only like 5% that consistently do (that might be being generous).
I can understand if someone on your right is driving slower than you…you shouldn’t change lanes twice just to pass them on the left; however, if you’re tailgating someone and both lanes on either side are open, use the one to the left. It’s common sense (and the rules of the road).
Obviously, people need a refresher course on the rules of the road. Pass on the left, use your turn signal, follow at a car’s length behind, change lanes at a safe distance (i.e. not when someone’s in your blind spot), don’t change lanes at an intersection (this includes turns)…really, just don’t be stupid (well, then no one would have driver’s licenses).
Sometimes I think we’d be better off riding horses. No one ever got hurt riding a horse (oh wait…).