[Significant Update: OK, now I'm really frosted! Steve began investigating this story, because it sounded just so fantastic, and he discovered that the Snopes-Web-Page link enclosed here features another link that sends readers to a false IMDB Web Page regarding the supposed Poseidon Adventure movie directed by D.W. Griffith. If you go over to the real IMDB Web Page on D.W. Griffith, however, you quickly discover that he never directed such a movie, and indeed, that no such movie EVER EXISTED! Damn! When you can't trust the Web Sites intended to debunk common myths, who can you believe? I'm complaining to Snopes! Meanwhile, I'll let this post remain, as a monument to my gullibility!]
Noel noticed this over at Snopes:
... The next evening -- the Titanic's last, as it turned out -- the entertainment switched to another 1911 film with a nautical theme, this one the work of an actor/director who was one of young Hollywood's fast-rising stars: D.W. Griffith. The movie was The Poseidon Adventure (unusual in its time for its length -- an amazing 53 minutes in an era when the 10-minute one-reeler was still the norm), about a group of six passengers and crew members who struggle to stay alive after the ocean liner in which they're travelling is capsized by a tidal wave.
... The Titanic's passengers, obviously unaware of the doom presaged by the film they were viewing, were so enthralled by the events of the The Poseidon Adventure that they failed to notice the slight shudder that marked the Titanic's fatal encounter with an iceberg at approximately 11:40 P.M. ... So enthusiastic was the audience's reaction to the film (and so slow was word of the true nature of the Titanic's dire condition in spreading) that The Poseidon Adventure was immediately screened for a second time just after midnight.
Ultimately, the grim coincidence of a film about a sinking ocean liner's being shown aboard a sinking ocean liner may have cost some passengers their lives. ... By the time the second screening drew to its conclusion after 1:00 A.M. and a few hundred Second Class passengers filtered back out on deck and finally learned of the Titanic's plight, all but a precious few of the woefully inadequate number of lifeboats had loaded and cast off ....