Just to alert those not in the know - if you were in the audience and were entirely confused when two characters dressed in black appeared, the tall skinny one says something to Gale, and half the people around you laughed, you clearly haven't watched enough good films. Those characters are Jay and Silent Bob from Clerks, Mallrats, Chasing Amy, and Dogma - four fantastic films from Kevin Smith, who plays Silent Bob. Go and see them. Now.
And again in this movie there's a small part for the man himself, Wes Craven. He's the guy with the video camera walking by Jay and Silent Bob. He even takes a good look at the camera.
Kevin Williamson (who had written the first two films, as well as the fourth) had an entirely different plot in mind, which he had outlined and given to the studio, only for it to be passed on. His original concept had the killers in the film be members of a "Stab" (the film-within-the-film) fan-club, who orchestrated the murders in order to gain fame and become heirs to Sidney Prescott's status as the soul-survivor. Aspects of this unused original story treatment were re-written into the fourth film, which features a killer whose motivation is fame and becoming the soul-survivor.
When Sidney is walking onto the set of her room there is a "Creed" poster. Creed is the band whose two songs, "What If" and "Is This the End", are on the movie's soundtrack.
In the early days of production, they had originally planned for Angelina Tyler to be the second killer, but this plan was scrapped before filming began.