I remember seeing Kirk Douglas in 20,000 Leagues under the sea and whatever turtle/charango kind of thing he was playing I could tell those were real chords. Also in Breakfast at Tiffenys , Audry Hepburn was playing real chords on her guitar when she was sitting on the fire escape. I don't know how much either one of them played other than that.

And what the heck is the name of the guy that stars on Third Rock From the Sun? He was in The World According to Garp. I've seen him play some pretty mean banjo a couple of times.