Book and movie titles fall in a gray area in U.S. law. For instance, although a book or movie is protected by copyright, its title isn't. Copyright simply doesn't cover titles.
And even if the title is distinctive, such as The 40-Year-Old Virgin, courts and the Trademark Office say it can't be registered as a trademark, even though distinctive words and slogans can be registered as trademarks in other contexts. There's an exception for series titles, such as Harry Potter, but that's of no help to single-work titles.
The rule against trademark registration purports to be absolute, and has been in place for at least 55 years. Nonetheless, I've developed ways to protect single-work movie titles using trademark registration -- effectively circumventing the long-established rule.
Back in 2008, I wrote a short article on the subject, in relatively plain English. It was the cover story in Los Angeles Lawyer magazine and continues to be widely read and requested. Click the link and check it out, or at least look at the picture on the cover and the amusing illustrations the magazine added.