I was glad to see that I am not the only one bothered by musical anachronisms in films.
When I mentioned that Johnny Cash wouldn't have been playing a Martin with a black pick-guard in the 1950s as in the movie Walk The Line or Woody Guthrie wouldn't have been playing a Mossman guitar as he did in Bound For Glory, my non-musical friends tell me I'm being petty, but these same friends would "have a cow" if someone was pictured driving an Edsel in a movie set in 1950.

I must mention to Linn, that a common expression among my friends in the sixties was, "Well, that really throws a fuck into our plans." I don't think the word's usage is as recent as you might think.