The title character was based on the author's daughter, Kathy Kohner-Zuckerman, and her adventures growing up in the surf culture on the beach at Malibu in the 1950's. As of this note (July 2006), she is 62, petite, healthy and attractive and living in Pacific Palisades with her husband of 42 years. And yes, there was a "Moondoggie", who still lives in California and is an artist.
In one scene as Gidget's father and mother are waiting for her to return, her mother says to her dad, "Who did you expect, Kim Novak?" Her dad had played "Howard Bevins" in Picnic (1955), starring Kim Novak.
James Darren was originally not selected to play Moondoggie because the role required two songs to sing and Darren was not well established as a singer. On his own, he cut a single with the studio's recording subsidiary Colpix Records which charted. Columbia changed their minds and gave him the role despite the fact that he couldn't surf and was a weak swimmer. He became a huge teen idol and subsequently repeated the Moondoggie role in Gidget Goes Hawaiian (1961) and Gidget Goes to Rome (1963), with two other Gidgets: Deborah Walley and Cindy Carol.
James Darren, Cliff Robertson, Tom Laughlin, and Doug McClure all appear bare-chested in this movie. In fact, Robertson's many shirtless scenes, showing him sun-bronzed and sweaty, easily constitute the best "beefcake" of his long movie career. Unfortunately, the normally very hairy chested James Darren was forced to submit himself to a complete body waxing which seems unnatural and out of keeping with his personality.
Cliff Robertson grew up in La Jolla California where he is well known for his surfing ability. Robertson can be clearly seen surfing in the movie. However, during a 1978 60 minutes interview Tom Laughlin admitted he suffered tremendously during the surfing scenes.