The Pros and Cons of Book Trailers

Here's an interesting New York Times article by Pamela Paul on the pros and cons of book trailers. These days, it seems to be a necessary element of book publicity, but how effective is it, really? What do you all think?
http://www.nytimes.com/2010/07/11/fashion/11AuthorVideos.html?_r=2&ref=books