Melanie Wilkes is described as a plain girl in the book and is liked because she is kind and sweet to everyone. Olivia de Havilland is far too pretty to be believable as a plain girl, but she is easily believable as the kind Ingenue that everyone loves.
Scarlett also isn't remotely beautiful in the book. She's decent looking but her appeal comes from her personality and lack of attainability. Vivien Leigh might be too pretty but she captures Scarlett's personality to the T. The original author gave Leigh her stamp of approval.
Adored by the Network: AMC loves to air this around Thanksgiving, even though it has nothing to do with the holiday and isn't really the kind of movie that appeals to all ages.
Beam Me Up, Scotty!: "Frankly, Scarlett, I don't give a damn." It's actually "Frankly, my dear, I don't give a damn." Also changed from the book, where its "My dear, I don't give a damn."
Billing Displacement: Vivien Leigh, a relative unknown, was billed the last of the four leads on the initial poster. This changed after she won her Oscar.
Creator Backlash: Very few of the cast members actually liked the characters they were portraying. Butterfly McQueen regretted playing such an Ethnic Scrappy, Leslie Howard felt he was too old for Ashley and hated the costumes, and Rand Brooks disliked playing Scarlett's first husband as he was a rough outdoorsman and disliked such a wimpy character.
Dawson Casting: Leslie Howard was 47, and felt he was far to old to play the twenty-something Ashley Wilkes. Justified because this film covers over ten years, and so he had to play the older Ashley as well. Also, Vivien Leigh was 26 years old when cast as the 16 year old Scarlett. Like the Howard example, this was justified as she continued to play Scarlett as the character aged.
Enforced Method Acting: When Melanie goes into labour, Olivia de Havilland had someone pinching her toes off camera to make her feel pain.
Money, Dear Boy: Clark Gable only agreed to do the film because the money would allow him to divorce his current wife and marry Carole Lombard.
Non-Singing Voice: Variation. The wretching noises Scarlett makes as she delivers her famous "with God as my witness" line were dubbed by Olivia de Havilland. Rumour is that Vivien Leigh either couldn't do it the way the director wished, or refused because it wasn't ladylike.
Playing Gertrude: Barbara O'Neil, who played Scarlett's mother, was only three years older than Vivien Leigh. She was twenty eight to Leigh's twenty-five. Granted the mother only appears in the part of the story where Scarlett is sixteen-seventeen (and Leigh plays her across several years) and young mothers were quite common in the South. But still very noticeable.
The Red Stapler: Uncertain, and definitely downplayed. Scarlett appeared in the top 1000 female names in 1940, a year after the movie came out, and lasted four years. The name reappeared in 1962 and 1963. It reappeared in 1992, then gained in popularity in the 2000s, reaching 30th in 2014.
Gary Cooper was the first choice for Rhett Butler. He turned it down, expecting the movie would flop. Margaret Mitchell's first choice was Basil Rathbone.
Alfred Hitchcock wrote a treatment for the scene where the women wait for the men on the raid from Shantytown at the request of the director. His treatment included precise shots, showing Rhett and Ashley dodging the Union soldiers - and a meaningful exchange of glances between Melanie and Rhett. None of this was used.
Judy Garland was heavily in the running to play Scarlett's sister Careen but she was too busy filming The Wizard of Oz - so Ann Rutherford was cast instead. Billie Burke, who played Glinda, auditioned for Aunt Pittypat but was turned down for being too young.
Early drafts of the script kept in Scarlett's son Wade but he was cut from the story before filming began. He still appears in a book of paper dolls about the characters that was printed before he was cut.
The final scene was to be of Scarlett clad in a green dress, approaching Tara. This was filmed (stills can be found on YouTube), but cut.
Of all the actresses considered for the role, Louise Platt, Tallulah Bankhead, Linda Watkins, Adele Longmire, Haila Stoddard, Susan Hayward (at the time using the name Edythe Marriner), Dorothy Mathews, Brenda Marshall, Paulette Goddard, Anita Louise, Margaret Tallichet, Frances Dee, Nancy Coleman, Marcella Martin, Lana Turner, Diana Barrymore, Jean Arthur, Joan Bennett and Vivien Leigh were given actual screen tests for the role of Scarlett O'Hara.
Hattie Mc Daniel was cast as Mammy after Louise Beavers, Etta Mc Daniel, Ruby Dandridge, and Hattie Noel were briefly considered.
Although Olivia de Havilland was always front-runner to play Melanie, Janet Gaynor, Fay Wray, Jane Wyman, Anne Shirley, Priscilla Lane, Marsha Hunt, Gloria Stuart and Andrea Leeds were also considered. Reportedly when Joan Fontaine was considered for the role, she rejected it but suggested her sister de Havilland for the part. Shirley, Hunt and Leeds were the only ones who underwent a screen test for the part.
Vincent Price, Jeffrey Lynn, Dennis Morgan, Douglass Montgomery, Wayne Morris, and Melvyn Douglas tested for the part of Ashley.
Betty Compson, Binnie Barnes, Evelyn Brent, Una Merkel, Glenda Farrell, Esther Muir and Ann Dvorak were among the actresses tested for the role of Belle Watling.