I think we watch movies because we want to see if the movie is any good before we see it, or we look and touch a dress or pair of shoes before we try them on and usually buy them (well i do, once I try something on ... I'll probably buy it)
The only thing we can't really do is read a book or a magazine before buying it, because wants we handle a new book we're devaluing it. Even when I'm at Borders if I'm planning to read over a coffee, I'll buy the book before hand. I once spilt coffee over a book I hadn't bought yet and then went to buy it and the man at the till told me that rarely happens, people read the book, dirty it or spill on it and leave it there.
So... how do we tell if we like a book before reading it? The cover makes it harder to tell, some covers are just really colourful or have an egg on it like Glue by Irvine Welsh which I do not think mentions and egg once or the blurbs sometimes don't say much.
So i think book trailers are a great idea, it's innovative, talks about the book and its characters and I think if I like the trailer I'm the type to buy the book (and see the movie, buy the dress and the shoes) I'm such a consumer!
I looked at book trailers and I found the best ones on You Tube. I found Jodi Picoult and Jen Lancaster and Marcus Zusak as well as unknown authors so I think book trailers are an excellent marketing tool ... have a look at The Bookthief -
Here's a list of the Top 20 books of 2007 and Stephenie Myer's Twilight
I'm liking this very much!