Trivia: At the very end of the film, when the group uses the Improbability Drive to go to the Restaurant at the End of the Universe, there are a lot of images that flash onto the screen when the drive is activated, so in the other parts of the film. In this case, the very last image shown is the face of Douglas Adams, the creator of the Hitchhiker series.
Trivia: In the planet construction facility, one of the planets resembles Douglas Adams's face.
Trivia: The leader of the demolition crew that comes to tear down Arthur's house has an Asian appearance, a vaguely Mongolian mustache and a round hat. He is straight from the book, where the character is a descendant of Ghengis Khan. He hates his life and has visions of hordes of Mongols laughing at him.
Trivia: The logo of Apple Computers can be seen just above Deep Thought's eye. Douglas Adams bought the first two Apple MacIntosh computers sold in the U.K. and remained a devoted Mac user for the rest of his life.
Trivia: Be sure to stay for the credits. About half way through there is a final Guide entry.
Trivia: As they enter the temple of the Jatravartid people of Viltvoldle Six, at the base of the stairs is a "perfect recreation of Douglas Adam's nose" (DVD commentary) modeled from a cyber-scan of this head that had been previously created for a game and used in the film as an homage to him following his death prior to the completion of the film.
Trivia: The message from ancient Magrathea was designed so that Simon Jones' head will appear in 3-D if the viewer happens to have a pair of old 3-D glasses on hand. (Stated on the DVD commentary track.)
Trivia: The woman in the street sitting reading a newspaper and ignoring the Vogons is Douglas Adam's mother.
Trivia: During the early 1980's, Ivan Reitman was working with author Douglas Adams to make "The Hitchhiker's Guide to the Galaxy" into a film. However, the project fell apart when Reitman decided to work on another film instead - the film that would eventually become "Ghostbusters." The "Hitchhiker's Guide to the Galaxy" movie didn't finally come out until over twenty years later.
Chosen answer: Because it was a radio show originally, Douglas Adams would write broadcasts from show to show. He did not know where something would lead, which let the plot become random and funny. So ultimately it was originally created to be funny, then he found a way to link it back in later.