I thought you'd all like to take a look at this blog that's currently being written by George Huffstutter, an ad agency guy that's been working in the industry for a bunch of years. He currently talks about advertising your book through 'roadblocks', which seems to be a way of inundating you with ads so you can't get away from it.
J.A. Konrath thinks that advertising isn't cost effective for a book, while Tess Gerritsen thinks it does. I don't know enough about it all to say anything useful. But it may be something food for you guys to peruse, in any case.