Renowned astronomer Seth Shostak was hired as a consultant on the film. He reviewed the script several times for errors, and gave suggestions for making the scientists less dry: "Real scientists don't describe an object entering the solar system as 'notable for the fact that it was not moving in an asteroidal ellipse, but moving at nearly 3*10 to the 7 meters per second'. More likely, they would say that there was 'a god-damned rock headed our way!'" He also noted the scientists should refer to one another by a first name basis.
According to the filmmakers, John Cleese was the most difficult choice in casting as he was primarily noted for comic roles. Cleese felt that at his age, a dramatic role with subtle humour would be an easier role to play rather than another manic old man.
In Harry Bates' short story 'Farewell to the Master', upon which the movie is based, the last line revealed a dramatically different angle. It reads: "'You misunderstand,' the mighty robot had said. 'I am the master.'"
When Javon is watching TV at Professor Barnhardt's house, it shows various pictures of riots around the world. One shot shows actual riot footage from Serbia on October 5th 2000, the day Slobodan Milosevic was overturned. A large crowd is in front of Serbian Parliament. Smoke is visible because part of building was on fire.
The design of Gort is similar to his original portrayal in The Day the Earth Stood Still (1951), but Gort is now a biological form rather than mechanical, as Scott Derrickson considered some extraterrestrial races would develop advanced biological forces instead of technology.
Gort's trademark eye beam is used twice in the entire movie. The first time to cause all electric to go out in the area when Klatuu is shot in the beginning of the movie and the second time to destroy the two drones and the sidewinder missiles that they launched to try to destroy him.
In The Day the Earth Stood Still (1951), Klaatu instructed Helen to say the famous line "Klaatu Barada Nikto" to Gort in the event of his death, which she did. In this film, Klaatu himself says the famous line to Gort shortly after arriving on Earth, after being shot by the army.
The orb was supposed to be filled with white limbo light, but Scott Derrickson felt the concept would then be unoriginal and changed the colour to greenish, a more appropriate colour for an environmentally conservative race.
Klaatu uses the phrase "tipping point", which is a climatological term meaning the point at which the reversal of climate change becomes impossible. Some scientists believe that this has already happened.
The words "Klaatu Barada Nikto", which are in the original 1951 film spoken by Helen Benson to Gort the robot, has featured in many other productions, for instance in Army of Darkness (1992), where they are the spell Ash must speak to stop the undead army from appearing.
The DVD and Blu-ray disc release of the film come packaged with a disc containing the original classic. This is a new disc, and does not contain any special features, although the copy packaged with the Blu-ray of the 2008 film is also a Blu-ray disc.
The coordinates for the "Impact Location" that appears on the big screen (Lat 40.75136, Long -73.98712) falls on the The Haier Building, 1352-1362 Broadway, at the corner of W. 36 St., in Midtown Manhattan. The building used to be the headquarters of the Greenwich Saving Bank from 1833 to 1981.
As part of the German (and probably too in other countries) promotional campaign, advertisements changed the title of the film to include the name of the city where the ads were published (i.e. "The Day Cologne Stood Still").
In the final scene, the Sydney Opera House and Sydney Harbour Bridge can be briefly seen from the point of view of Mrs Macquarie's Point - the same park used for the final scene of Keanu Reeves's other sci-fi-apocalypse story, The Matrix Revolutions (2003).
The trivia item below may give away important plot points.
Klatuu used the famous line, Klatuu Barada Nikto twice in the movie, at the beginning after he is shot by the military, to stop Gort from hurting them and then at the end of the movie when Klatuu touches the sphere and says Klatuu Barada Nikto to stop Gort, who now is in the form of the Nanobots, from destroying the world. Once he touches the sphere and says, Klatuu Barada Nikto, the nanobots all die.