Disney discovered that the shooting schedule at Mount Rushmore would displace the local Hill City High School prom that is held annually at the location. To make up for this, Disney paid for the prom by providing transportation to a new location in Rapid City, door prizes at the prom, and scholarships for the valedictorians.
The document briefly seen in Riley Poole's (Justin Bartha) book is an autopsy report for Marilyn Monroe. Certain conspiracy theories prevail that Monroe was murdered because of an illicit affair with President John F. Kennedy.
The night before the scenes at the University of Maryland were to be filmed, a half inch of snow fell. The crew then had to use fire hoses to hose down the entire McKeldin Mall and nearby locations to melt the snow for continuity in the movie.
While examining the lost page of the diary, the "historians" say that John Wilkes Booth studied Latin because of the writing in the diary and the fact that he said, "sic semper tyrannis", after shooting President Lincoln. Real historians (or screenwriters) should know that John Wilkes Booth, along with his brother and father, were famous actors and their best known performance was of William Shakespeare's "Julius Caesar". In that play, the character of Brutus yells, "sic semper tyrannis" just before the famous slaying in the Senate. John Wilkes always wanted to play Brutus, but his father never let him, instead picking his brother Edwin for the role. It seems that John Wilkes did eventually get to say those famous lines on stage.
The guy who gets his car stolen by Ed Harris in London is the same guy who got his Hummer stolen by Sir Sean Connery in The Rock (1996), another of Jerry Bruckheimer's movies which also starred Nicolas Cage and Ed Harris.