John Lennon's murderer Mark David Chapman loved this book and claimed to use it as an inspiration for committing the murder. Whilst this certainly helped the already considerable controversy surrounding the book, it also meant that many later readers approached the work expecting it to be more brutal, violent and dark than it necessarily is.
John Hinkley Jr., who tried to kill Ronald Reagan, had a copy in his hotel room. He's been reported to be obsessed with it, but that might just be in confusion with Mark Chapman. It doesn't help that Conspiracy Theory featured the link between the two assassins and the book as a plot point.
Robert John Bardo, who shot and killed actress Rebecca Schaeffer, was also carrying a copy of the novel when he committed the murder, and threw it on a rooftop as he fled. However, he insists that this was a coincidence, and that he was not trying to emulate Chapman.
More recently, Seung-Hui Cho, the shooter in the Virginia Tech Massacre, sent videos to news agencies in between the two bouts of murdering. One of these videos included a rant of how he related to The Catcher in the Rye.
It got to the point that the Mel Gibson blockbuster Conspiracy Theory made it a plot point that government-trained assassins were brainwashed into buying copies of "Catcher In The Rye" as a tracking method. It's become THAT ubiquitous.
What Could Have Been: This has been proposed for a film adaptation dozens of times, all of which were personally turned down by Salinger. Ralph Bakshi wrote a personal letter to Salinger proposing that he purchase the rights and make it into an animated film with live-action bookends. Salinger told Bakshi that he didn't feel that the novel was fit for any other medium.