There've been a number of discussions around the blogosphere recently about book trailers -- Romancing the Blog had one today and has had others in the past, and they've been a subject of discussion in other places as well. I've never seen a good one, but then I'll admit I haven't gone looking very much. Even granting that there are good book trailers, though, I still have to wonder how much correspondance there'd be between a reader's enjoyment of a trailer and their enjoyment of the book it's advertising.
Movie trailers work because the trailer -- a piece of video with bits of scenes out of the movie, dialogue from the movie, action from the movie, showing the actors who are in the movie, and playing music from the movie -- give the viewer a small sample of the experience they'll have while actually watching the movie. "Like this? Get more of the same!" is the message of a movie trailer.
Book trailers, though, present information in a mode completely different from that of the book itself. Even a well-done book trailer, with hired actors or custom animation rather than pans of stock photos, and with music appropriate to the mood of the book, is going to be presenting an experience which bears very little resemblance to that of actually reading the book.
So how valuable is the trailer going to be, from the POV of the reader? I love watching movie trailers because I can get a feel for the movie and decide whether I want to see it. It doesn't always work -- we've all seen trailers where it turns out that all the best parts of the movie were in the thirty-second trailer -- but if I like the chase scene or the effects or a bit of dialogue in the trailer, I'll probably like it in the movie too. Liking the actors or the music or the visuals in a book trailer, though, doesn't really tell me whether I'll enjoy the experience of reading the author's writing in the book. (Although it might suggest that I'd enjoy watching a movie made from the book.) And although a trailer can certainly present a short description of the plotline, which is more relevant, I can get that just as easily and without all the extraneous distractions by reading the back cover blurb of the book itself.
If I do buy the novel being advertised, I'm not going to be watching the actors act it out, nor am I going to have the music playing. I'm going to be reading the writer's words, and all the voices, music, action and animation is going to be provided by my own mind, as suggested by the text. It's quite possible that I might enjoy a trailer very much but not care for the book for whatever reason, because the experiences of each are very different and liking one isn't going to necessarily guarantee liking the other. So from my POV as a reader, how much benefit is there to watching the book trailer if, when it finishes playing, I'm still no closer to knowing whether or not I'd enjoy reading the book?
If a writer only has one book to sell, then I suppose this doesn't matter. If a trailer persuades me to buy the book, then that's the whole point, right? The writer can smile and bank the money (after paying the people who made the trailer) and there you go. But maybe I would have liked their second book, or their fifth book. I'm less likely to buy those books, though, because at this point I have personal experience telling me that liking Author X's marketing doesn't mean I'll like Author X's book. I thought the trailer was great but disliked the book anyway, so if I like the marketing for the next book -- even if it's a more traditional blog or magazine ad -- my experience is telling me that I'll probably dislike the book it's pushing, that Good Marketing = Bad Book in the case of Author X. Yuck.
I might be wrong about this, and it's possible that five years from now we'll all be scrambling to make trailers even for our short stories. As a writer, though, I'm not going to jump onto this bandwagon without a lot more data, and it'll have to show that there's a significant correspondance between readers liking the trailers and liking the book, not just that watching the trailer makes them buy the book.
As a reader, I'll stick with the written modes of marketing to decide whether or not to buy books. At least there I have some idea of what I'll be getting.