I spent seven weeks in Florida hour building with my school, and we didn't need a visa. We were told to say to the passport people (or whatever they're called), that we were there for pleasure. I was told some years earlier a girl had gone there, and told them she was training to be a commercial pilot, which lead to a long interview! Poor girl.
But if you're going on holiday, just don't mention the fact that your flying, they don't need to know and your not doing anything wrong. Enjoy!