Check out the book trailer for Stephen King's Under The Dome, which plays like a splashy Michael Bay preview. Does it make you want to read the book? Laura Miller at Salon suggests some trailers make books less enticing.
Miller's piece points to several uninspiring book trailers for non-science fiction books, and actually singles out the trailer for Scott Westerfeld's Leviathan as a rare example of the good book trailer. Writes Miller:
A visit to a dedicated trailer site like Book Screening or a search for "book trailer" on YouTube reveals just how many of these videos there are, and a random sampling will quickly convey a sense of the low average quality. Typically, a trailer will open with text, fade to a stock photograph or a bit of vague footage (clips of bad weather seem particularly popular, as a metaphor for emotional intensity, no doubt), then back to text and so on. Good voice and acting talent can be expensive, as can effective music, so either the soundtrack comes from a pal strumming lamely on a guitar or it's been "borrowed" from a copyright holder who will, it is hoped, remain none the wiser. Some trailers are so rudimentary they're just a still shot of the cover attached to an audio recording of a live reading. Anything more ambitious can cost the hopeful author as much as $3,000.... True, there are (a few) good book trailers as well as (many) unbelievably wretched ones, but who really chooses a book on the strength of a trailer?
I'd say that there are indeed a number of wretched book trailers out there, but a decent trailer can spur some interest in your book that might otherwise slip through the cracks. (Exhibit A: Jeff Carlson's Plague Year.)