The scare was that the valves would wear themselves into the head. I think it was Hotrod that did an article on hardened seats years and years ago, their conclusion as Jerry said, unless you are running at high RPM all day long (like going down the freeway across the country and/or pulling a good load) it will take years to sink the valves into the head, and even then, it was a heck of a lot of years, and they were talking about a V8 with a bigger cam and heavier springs than most of the stovebolts are running. I would not worry about it unless you are driving cross-country or putting 20-30K miles a year on it.
