The concept of Sally being a picky eater was based on Nora Ephron, the scriptwriter, and so years after the movie came out, when Nora Ephron was on a plane and ordered something very precise, the stewardess looked at her and asked "Have you ever seen the movie 'When Harry Met Sally'?"
The segments of married couples telling the stories of how they met are real stories that Rob Reiner collected for the film. Actors relate the stories.
In an interview with National Public Radio on 2 November 2004, Nora Ephron credited Meg Ryan not only with the idea of faking orgasm in the well-known restaurant scene, but also with the idea of setting it in a restaurant in the first place.
When Harry and Sally drive from the University of Chicago to New York, they should drive on the Lake Shore Drive heading to the south (to the direction of Gary), not to the north (to the direction of downtown). So they should not be on the Lake Shore drive on the north of downtown.
When Sally is faking the orgasm in Katz's Deli, the woman who says "I'll have what she's having" is seated in the self service section and a waiter would not have come over to take here order. The waiter service section is against the wall to Sally's left.