Interesting about the motorcycle
That was obviously Warren Beatty riding his motorcycle in those scenes, as opposed to a stuntman, but what I find interesting is that the insurance company would allow Beatty to do that; would any insurance company underwrite a major motion picture today with the star of the picture riding a motorcycle without a helmet? Hell, even Peter Fonda wore one in "Easy Rider" and that was made before (and depicts the same time period) "Shampoo" (granted, Dennis Hopper didn't wear one in "Easy Rider", and he was not only the co-star, but the director as well).
The thing about a helmet is, safety issues aside, a full-face helmet allows the filmmakers to use a stuntman and no viewer is the wiser.
Yes, I know Steve McQueen didn't wear a helmet in each cycle scene in "The Great Escape" (he had a German soldier's helmet on in a couple) but Bud Ekins did the famous cycle jump over the fence.
The only more recent example I can think of is Tom Cruise in "Top Gun".
I'm just surprised that a star would be allowed to do that. Does add a nice touch of realism, though.