A good deal of the shots in the film depicting "Harvard's Campus" were in fact filmed at Johns Hopkins University in Baltimore, including the opening scene in the trailer for the film.
Mark Zuckerberg thought the movie was "interesting" as he said when he met Jesse Eisenberg, who portrayed him in the picture, on Saturday Night Live: Jesse Eisenberg/Nicki Minaj (2011), when Eisenberg was hosting.
At one point in the film, Bill Gates gives a speech to a class of Harvard students, including Zuckerberg. Even though the character both looks and talks like Gates, it's not him; it's actually a "professional Gates impersonator," But his voice was dubbed by a "24-year-old African American kid with dreadlocks," who just happened to sound like Gates.
Armie Hammer studied Jeremy Irons' performance in Dead Ringers (1988) to get an idea of how to play twin brothers.
The real Mark Zuckerberg had never heard of an Appletini before he had seen the film. After he tried one, he liked it so much he made the Appletini Facebook's official drink.
The sequence where Mark Zuckerberg leaves a classroom and meets the Winklevoss twins in the hallway was filmed at the University of Southern California in Los Angeles. The classroom he exits is in a different building (Taper Hall of Humanities) from the hallway in which he meets the twins (Grace Ford Salvatori Hall).
Jesse Eisenberg, who is diagnosed with Attention deficit hyperactivity disorder, said in an interview that one of the hardest things about the role was having to deliberately speak and behave in a manner he had struggled against in his own personality his entire life.
The note "U dick" that Mark is handed by a girl in class is a replacement of a more profane word that the MPAA wouldn't approve for a PG-13 rating.
Reported to be R-rated during production, but end up editing down to PG-13 to make it accessible for a wider audience.
David Fincher's favorite line in the film is, "I'm just checking your math on that. Yes, I got the same thing."
Alfred Molina was considered for the role of Lawrence H. Summers before Douglas Urbanski got the part.
The line about Cameron Winklevoss and Tyler Winklevoss going after Mark Zuckerberg like the Cobra Kai kids going after Ralph Macchio in The Karate Kid (1984) was something they'd said to Ben Mezrich during his research interviews for the book.
The real Lawrence H. Summers called the film's portrayal of his meeting with the Winkelvoss twins "fairly accurate". He went on to say "I've heard it said that I can be arrogant. If that's true, I surely was on that occasion. One of the things you learn as a college president is that if an undergraduate is wearing a tie and jacket on Thursday afternoon at three o'clock, there are two possibilities. One is that they're looking for a job and have an interview; the other is that they are an asshole. This was the latter case. Rarely, have I encountered such swagger, and I tried to respond in kind."
Aaron Sorkin and David Fincher wanted to do the movie based solely on a 14-page book proposal that somehow got leaked to Gawker.com right about the time 21 (2008) came out; the book hadn't even been written yet, and Ben Mezrich wound up writing it in a hotel room with Sorkin right next to him, handing Sorkin the chapters as they were finished.
Amy's line in French ("Tu fais l'amour a la jolie fille") roughly translates in English, "You've made love to a pretty girl."
During the night club scene the extras are miming their dancing and the music was added in post-production. Jesse Eisenberg and Justin Timberlake had to shout their lines as though they were talking over the music. Eisenberg said it was a challenge to not lose their voices.
There is actually a Facebook page for "Erica Albright," a character in the film. The profile pictures are of the actress Rooney Mara who plays Albright. It is also listed that she attended Boston University.
The notepad that Mark Zuckerberg carries in the deposition scenes was Jesse Eisenberg's own idea, as part of his way of assessing his own performances after each take.
Despite the fact that director David Fincher has been a big proponent of digital filmmaking since his 2007 film Zodiac (2007), this is his first film to have been completely shot digitally (both Zodiac and The Curious Case of Benjamin Button (2008) had certain shots/segments shot on film).
When Facebook hits one million members, the number 1,000,046 appears on the screen after Sean Parker requests a refresh. The producers purposely chose the number to correspond with the running time of the movie at 1:46:46.
After Mark Zuckerberg finishes the coding marathon in his dorm room, he then closes his eyes and slowly moves his head back and forth, and Eduardo asks him, "Mark, are you praying?" On the DVD commentary, Aaron Sorkin explained that what Mark was doing was davening, a word that comes from Yiddish and which generally refers to prayer in Judaism, but which also specifically refers to the type of head and body movements that Jews traditionally make while praying. Sorkin mentioned on the commentary that he considered writing Eduardo's line as "Mark, are you davening?" instead of "Mark, are you praying?" to make it clearer to the audience what Mark was doing.
Shia Labeouf turned down Jesse Eisenberg's role.
At the time of release, there were about 750 million active users on Facebook. If everyone who had a Facebook account at the time went to go see the movie during its theatrical release, it would have grossed somewhere around US $6 billion.
Natalie Portman revealed during "Newsweek's 2011 Oscar Roundtable" that she gave a dinner party for writer Aaron Sorkin, while he was writing the script for this movie, to which she invited a bunch of her friends from Harvard. She wanted to give him the chance to listen to first-hand stories about the social life at Harvard University.