The orgasm scene was filmed at Katz's Deli, an actual restaurant on New York's E. Houston Street. The table at which the scene was filmed now has a plaque on it that reads, "Where harry met sally... hope you have what she had!"
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 see the movie 'When Harry Met Sally'?"
Sally's picky and crazy eating habits were put into the movie after Rob Reiner saw Nora Ephron ordering her food in the same way Sally did in the movie. When Rob brought this up, Nora said, "I just like it the way I like it," a line which was put into the movie.
Rob Reiner, Nora Ephron, and Andrew Scheinman chose beautiful locations to highlight the characters lack of insight - Harry and Sally are as blind to romance as they are to the love growing between them. The same logic was used for Harry's apartment. The windows overlook the Empire State Building. It could either the loveliest - or - loneliest, view in the world.
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.
Harry is somewhat based on Rob Reiner. Rob was depressed, and loved being depressed, like Harry Burns in the film. Sally is somewhat based on Nora Ephron. Nora is optimistic, cheerful, loves control, and is the type of person who is "just fine" with everything, just like Sally Albright.
For the infamous orgasm scene, the original script called for just Harry and Sally to talk about women faking an orgasm, until Meg Ryan suggested that Sally actually fake an orgasm at the table. Rob Reiner loved the idea and put it into the script.
The quote "I'll have what she's having" was not only voted #33 on the AFI's list of "Best 100 Movie Quotes in American Film", and the ONLY quote on the list to be spoken by a non-professional actor (it was director Rob Reiner's mom who delivered the line). Furthermore, it was the only quote on the list which was the ONLY film dialogue ever uttered by the actor who delivered it.
While writing the script, Rob Reiner once said, "You know how women have a base of makeup, I have a base of depression. Sometimes I sink below it. Sometimes I rise above it." Since the Harry Burns is based on the depressing Rob, Nora Ephron threw the line into the script, which Rob cut somewhere along the line.
Before deciding on the title, "Just Friends", "Playing Melancholy Baby", "Boy Meets Girl", "Blue Moon", "Words of Love", "It Had To Be You", "Harry, This Is Sally", and "How They Met", were considered by Nora Ephron, Andrew Scheinman, and Rob Reiner.
During the end scene Harry mentions never understanding what the song Auld Lang Syne was about. Some years earlier Director Rob Reiner also questioned the meaning of the song when portraying Mike Stivic on an episode of All in the Family (1971).