interesting topic. it takes a good engineer, that knows their machine, to properly track and balance each type of helicopter. And then it takes an owner that wants, and is prepared to pay for, a smooth flight, and not just, oh well, its within limits "thats good enough."
we never accept "thats good enough" for very long, and spend a lot of time master balancing blades, getting the setup all right and T&B. In the older helis you also have to change out rod ends and bearings quite often, but it pays off with a smooth ride.
i took a guy for a survey a while ago, he wasn't happy that we "only" had a JR to do it in, he had been in JR's, 500 and 350's and said the JR was the worst, most bouncy, horrible machine to ride in. After we had done the job, about 6 hours of survey, he admitted that our JR was the smoothest helicopter he had ever been in, smoother than any 500 or 350 he had been in. Problem is, every minute in the air it is slowly working itself out of balance...