This question in this post doesn't really have an answer. I'm just throwing it out there because it's been on my mind ever since I started dreaming up different ways to market my own eBooks.
Have you ever seen a book trailer? I remember they used to be part of those VHS tapes played at Scholastic Book Fairs, particularly the ones for any Lemony Snicket book or Harry Potter installment. They usually employ animated images or paintings that attempt to give the illusion of movement, combined with animated tag lines and, finally, the reveal of the book cover and where to purchase it or find out more. Check out the trailer above for Divergent, which I am reading right now.
Do book trailers really get anyone's attention? My thinking is that they might, if you are someone who browses YouTube regularly. On Amazon? I'm not so sure. There are many more ways to get people's attention on the actual merchant site including book cover and description. But, for other sites? I'm guessing that the impact of having a book trailer on YouTube isn't very large unless you're Suzanne Collins with a built-in audience who is devouring anything related to your franchise, but something is better than nothing when it comes to indie publishers.
I've been collecting materials to make my own sixty second trailer, and it's a lot more work than it seems. First off, I have no money to spend on this kind of production, but thankfully I have a background in television and editing where the actual construction of the trailer won't be too horrible. I also have some skills in animating things (see my YouTube page for some examples) and I'm looking forward to making something that can broaden the scope of my marketing materials.
What I get out of a book trailer is an atmosphere. This tiny piece of video is trying to give me visually and audibly the feeling that the book will and should instill in me, should I choose to read it. Some book trailers are really elaborate - see any of Amanda Hocking's trailers. They're basically a full-blown, cast, acted trailer that looks like it belongs in a movie theater. I wish I could do that for my upcoming work, but the resources are beyond me. Perhaps for the sequel...
So, in conclusion (though I'm sure I'm not finished with this topic completely) I'd say that a book trailer has potential to bring in people who would not browse Amazon regularly. It's a good bridge from YouTube to your book's page or your website. It also makes you look more official, since the only big name authors I've seen to get book trailers consistently are Hocking and Stephen King. Anything that King does with his enormous publishing contract that I can also do for my own work is something that I'm interested in. It's all about your preference and how you want to look visually to potential readers. Another question to ask is how much time it will take you versus how much you will get out of it. It's all up to you.
Will it be worth it for me? That remains to be seen (and I also have to make the darn thing!). Look for a super snazzy book trailer on this blog and my YouTube page in the coming months!