Accidentally Correct Zoology: Skull Island apparently has a breed of theropod dinosaurs that developed batlike wings in lieu of feathers. Ten years after the film's release, a real theropod with a similar adaptation (Yi qi) was confirmed to exist, though it still has feathers.
Acting for Two: Andy Serkis plays both Kong himself and Lumpy (the ship's cook, barber, and surgeon).
Jamie Bell stayed in character throughout production, never lapsing out of his American accent.
Andy Serkis studied wild gorillas in Rwanda, picking up their movements.
Missing Trailer Scene: In the trailer, Ann is filming a scene from the movie and screams—only for Kong to scream back from far away. This is replaced by a different scene in the film; Ann screams for real when a man is killed in front of her. This is referenced in the video game adaptation where Denham films Ann screaming near the beach before something screams back—only that it's from the Giant Enemy Crab coming up from the shore instead of Kong.
Playing Against Type: Jack Black, best known for playing goof-balls, couch potatoes, and irreverent stoners, here portrays an obsessive manipulator driven by romantic ambition.
Prop Recycling: Peter Jackson owns several props from the original film, and put some of the items from his collection into this film. These items include Skull Island spears, and a brightly painted shield (seen in the cabins of the S.S. Venture) and some of the drums from the sacrifice scene (in use during the jig scene).
Saved from Development Hell: Peter Jackson's first attempt at a King Kong remake was in 1996, and looking at concept art and the first draft of the script, you can see a lot of similarities between the two. What would have been included in the 1996 version, just going on said script, would have been a pack of Carnotaurus in the role of the raptor-like Venatosaurus, a group of axolotl-like creatures instead of the Piranhadon from the swamp scene in the extended cut (one of which would have eaten Herb the cameraman alive), and Denham being an irredeemable jerkass. Apparently Jackson was never too terribly fond of the director character. Also, Kate Winslet would have played Ann.
Stillborn Franchise: It was revealed more than fifteen years after the movie's release that a sequel to the movie, tentatively called Skull Island, was proposed in 2013, with Adam Wingard as the director and Jackson intending to return as a producer. However, the film rights to Kong had changed hands to Warner Bros. at the time, complicating the idea of a sequel to a Universal-made movie, and the plan did not progress beyond a rough story outline (one of which was a prequel set during World War I, and another set in the present day) before it eventually evolved into the unrelated Kong: Skull Island (Wingard would get his chance to direct a Kong movie eventually with Godzilla vs. Kong).
Trolling Creator: Peter Jackson trolled viewers on April Fool's day by announcing via web diary that there was a Kong trilogy planned, and work was already started on Son of Kong and King Kong: Into The Wolf's Lair.
The film was originally scored by Howard Shore, but it was later removed from the film when Shore and Jackson agreed it didn't quite fit (hence James Newton Howard having to do a rescore at a very late stage—that's why three conductors and a small army of orchestrators are credited). Shore had already filmed his cameo as the orchestra conductor, however, and it remained in the movie.
Fay Wray herself was asked to deliver the last line in the film. At first she refused, then told Jackson, "Never say never," suggesting she was changing her mind. Ultimately, though, she died during pre-production and the line was given back to Denham as before.
Jackson has also admitted in the DVD behind the scenes that the climax would have had a different twist: Jack Driscoll, having a background in World War I as a fighter pilot, would have stolen one of the biplanes and shot down as many enemy planes as he could, though Kong would still fall to his death anyway. A version of this concept, where Kong lives after Jack shoots down enough of the planes, would be used in the 2005 video game based on the movie as a bonus alternate ending.
In an early draft of the screenplay, Ann Darrow was the daughter of a famed archaeologist, and Jack Driscoll was his assistant. Lord Darrow was killed in Ann's introductory scene by the Indonesian military in a cover-up attempt of his discovery of remnants of the Skull Island culture.
Jackson originally wanted George Clooney and Robert De Niro to play Jack Driscoll and Carl Denham respectively. Ian McKellen was offered the role of Ann's father, but he was doing a play in London and had to decline. De Niro would have been an Age Lift for the character, being well-past the character's thirty-five, stated as such in the original film's novelization.
Natalie Portman screentested for Ann Darrow, but was deemed too young for the part, despite being two years younger than Fay Wray had been.
Sylvester McCoy screentested for the role of Herb the cameraman.
Jim Jarmusch was approached to play one of the studio executives; the severe one with white hair seen in the final film even resembles him.
The ice skating scene between Kong and Ann wasn't in the original script. It was thought up during post production and added in afterwards.
Early ideas included shooting the film Deliberately Monochrome. An unlockable mode for the video game allows you to play it in Black and White.
Specific
There's a deleted scene in which the first time they hear King Kong's roar is after he's heard an acting scream by Ann while Denham's filming. This was put into the game.
There's an Ascended Extra for the game; Hayes stays alive much longer, and when he eventually dies it's by getting trampled by a V. rex.
