If children are our future ( which they obviously are) then book trailers are also part of the future of  book marketing.  I read a lot of online news sites and lately I have been noticing that story links are starting more and more to lead to videos. This is intensely annoying to me because I tend to view reading and watching as two different and separate entities -- this is one of the reasons I have so much trouble with foreign films, I simply cannot coordinate reading the subtitles and watching the films effectively -- it results in a very unpleasant viewing experience for me. This is also why I have so much trouble with graphic novels. But I am old and was not brought up to be visually oriented -- we did not learn visually when I went to school, we learned by reading and discussion-after we read and discussed, then visual reinforcement may have been added as a treat -- so evidently my brain has developed differently from today's people. Young people today are intensely visual, therefore we are getting more visual links on news sites, critical sites, blog sites. I viewed a few book trailers from popular teen books, Warm Bodies, Divergent, Poison Princess. They all had a high viewership ( not viral, but high). Warm Bodies and Divergent were extremely professional productions -- WB had striking and stark visuals accompanied by reading and written reviews, Divergent's was only about 45 seconds long, totally symbolic and visual with very powerful music. I also often view short book trailers on television and, I have to admit, sometimes the production does at least pique my interest in the book. I don't think that at this time book trailers are making a huge impact but I predict that they certainly will in the future simply because our new adults are innured to the visual in their learning process. That is why the young adult trailers are more popular than the adult trailers, different ages, different brains. I cannot see these advertisements as being particularly useful for RA. They certainly are not balanced criticisms of the book and the very, very visual ones do not convey much about the plot or characters. The book trailer for Poison Princess, however, was quite helpful in elucidating plot and characters because it was just a straight discussion by Kresley Cole about the origin and import of different plot elements -- so I guess it depends upon type of trailer, the ones which are purely visual or musical are of no help but author discussions and online critiques can be of value.