I was at a conference in the Plaza Hotel in New York a couple of years ago, so I asked the bartender in the Oak Room whether the Oak Room scenes in the movie had been shot there. He didn't have the slightest idea what I was talking about. But I got a videotape of the movie recently, which includes a documentary of the shooting of the movie. Turns out the Oak Room scenes were shot in a facsimile of the bar built in Hollywood.
The cropduster scenes were shot outside Bakersfield in California.