David Pogue of the New York Times initiates an interesting discussion about the liberties taken by movie makers in crafting trailers that don't exactly match up with the actual film. His primary example is "National Treasure: Book of Secrets," which if you compare its trailer to the finished product is apparently an exercise in deception more than a work of art. Pogue's solution? IMDB.
Personally, I'd be willing to accept this flimflammery if only the trailers would be shorter and fewer.