I freely admit--I'm terrible with titles. They either occur to me right away or I end up agonizing over them for way too long and go with something lame. However, after compiling a list of biographies and memoirs for a new site (details soon), I don't feel so bad. You would not believe the number of authors who couldn't let well enough alone after coming up with a catchy title and saddled the book cover with the longest subtitles they could think of.
For instance: We Bought a Zoo. Not the greatest title in the world but it tells you what you need to know about the story, But just in case a reader has reading comprehension problems, the author added this subtitle: The Amazing True Story of a Broken-Down Zoo, and the 200 Animals That Changed a Family Forever. Then, when the movie tie-in audio book edition was published, it got an even loner subtitle: the Amazing True Story of a Young Family, a Broken
Down Zoo and the 200 Wild Animals that Changed Their Lives Forever. That's a total of 26 words. A couple of other book titles matched that total but so far, I haven't found any that surpassed it. There were a lot of titles in the 20-word range though.
Makes me even more appreciative of one-word mystery titles. And here's a link to a column by Bill Morris about the Appeals and Perils of the One-Word book title.