Michelle Pfeiffer hadn't sung in a year when she got the part of Susie Diamond. She had to practice for ten hours a day in the studio, and then took the tapes home with her to study them. For her most famous scene, singing 'Making Whoopee' on Jeff Bridges' grand piano, it took six hours to shoot it. She only had one choreography lesson, and wore knee and elbow pads during rehearsals.
When Jack goes to Frank's house, he is dropped off by a cab from the "Bay City Cab Co." However, the movie takes place in Seattle, not San Francisco (the Bay City).
In the discussion in the car immediately after the Polynesian restaurant gig, Jack is wearing his tuxedo. They were wearing Hawaiian shirts on the gig however.
When Frank, Jack and Susie get underway for the trip to the New Year's event at the resort hotel (a.k.a. Bill Gate's house), they are first shown driving southbound on the Mercer Street onramp to Interstate-5. Then the scene shifts to them driving near the Spokane Street exit southbound, five miles to the south. Then the scene shifts back to them driving emerging from a tunnel, which is actually the same southbound I-5 onramp, only a little farther past the initial shot.