In one sex scene Lester (Jason Mewes) flips his tie around, so it's hanging down his back. This was done because Jason has director Kevin Smith's daughter's name tattooed down his back, and used the tie to hide said tattoo.
The stick figure poster came from a conversation between Kevin Smith and Seth Rogen. Kevin said that they'd might as well use stick figures, since that's all the MPAA would allow. Rogen said that would be funnier than the whole movie.
In the movie Zack and Miri are supposed to be the same age but in real life Elizabeth Banks is almost ten years older than Seth Rogen. At the time of shooting, Seth Rogen was three years from his high school reunion, while Elizabeth Banks would have had hers six years prior.
A portion of the plot is based on director Kevin Smith's experience making Clerks. (1994): a very low budget, working only with friends, using a hockey stick as a boom microphone pole, and shooting the movie at his job (the Quick Stop/RST Video in Clerks. (1994), and the Bean 'N' Gone coffee shop in this film).
The city of Philadelphia refused to allow the poster at bus stops because of the word "porno". When Kevin Smith agreed to have the word taken out and just have the title "Zack & Miri", the city still refused.
During the mid-1990s, Kevin Smith was commissioned by Warner Brothers to write a new Superman movie, the screenplay of which was eventually titled "Superman Lives." At one time, Tim Burton was attached to direct and Jon Peters was attached to produce the film. The project fell through in the late 1990s. The next attempt to resurrect the Superman franchise, however, was successfully made into a movie: Superman Returns (2006), starring Brandon Routh, who appears in Zack and Miri Make a Porno (2008) as Bobby Long.
"The other Zack" that Zack and Miri meet at their 10th High School reunion is supposed to be an old classmate of theirs. That should place the attendees at about the age of 28 years old. Kenny Hotz who portrayed "The other Zack" was 40 years old at the time of filming.
The City Of Toronto has slightly edited version of the original poster at most subway stations. Elizabeth Banks is smiling, and the alternate lowered version of her in front of Seth Rogen shows her forehead, implying she is not performing oral intercourse.
Kevin Smith originally wrote the film to be set in Minnesota, where he had shot Mallrats (1995) prior, and had stated a desire to shoot there again. However, for budgetary reasons, Smith opted to shoot in Pittsburgh, where he had shot Dogma (1999), and re-wrote the script to take place in Monroeville, Pennsylvania.
Jeff Anderson enjoyed that, as opposed to the verbose Randal that he played in Clerks. (1994) and Clerks II (2006), the character he played in this film, Deacon, appears in a lot of scenes but yet doesn't have a lot of dialogue.
The mention of fleshlights in this film was not product placement. However, fleshlight would go on to sponsor Kevin Smith's Smodcast/podcast network and get many endorsements from Smith himself who claims he, "keeps several around the house."
Near the end of the film there is a scene where Traci Lords is seen on a rotating bed, spanking two of her co-stars with a riding crop. This is a parody of the final scene in the film that was at the center of Traci's notoriety in the '80s: New Wave Hookers.
The movie's original poster was deemed too explicit by the MPAA and was banned in the US, because it suggested the characters on the posters are engaging in oral sex. It featured two separate images of Seth Rogen and Elizabeth Banks, who are fully clothed, and the back of the actors' heads close to each other's crotch.
The trivia item below may give away important plot points.
At the reunion, Zack II's full name is Zack Knutson, a reference to Zak Knutson, who played the Sexy Stud in Clerks II (2006). Zak can also be seen as a cameraman in the scene during the credits of Z&M.