Trend slave that I am, I've decided to join in on the book trailer craze by asking my twelve year old to put one together. I think she did a wonderful job, especially considering she was working with a budget of $0 (some of the fancy ones I've seen must have cost many thousands with impressive graphics, animation, sfx, live action, etc.). She used Windows Movie Maker, public domain photos (except for the cover), and creative commons licensed music.
I'm not convinced that book trailers "work," nor, obviously, that it's a good idea to spend a lot of bucks producing one, but I do place them squarely in the "It couldn't hurt," column.
What do you think about book trailers? Help? Hindrance? Meh? Has a book trailer ever tipped the scales in favor of you buying the book? Let us know in the comments.