I think Stephen King's books to movies indicates what can happen when best selling (and loved) books are made into movies. Either the director/studio does whatever the hell they want until the finished product does little more than share the same title with the book, or the author-who-isn't-a-director takes control and tries to preserve the integrity of the book at the expense of a quality movie product....
There are exceptions, of course. I'm hoping it indicates a move from Hollywood to actually attempt to follow a book's premise in the same way they finally got it through their thick money-or-nothing heads that they needed to be respectful of the comics they were making into movies.
I remember Anne McCaffrey making a comment at Dragon*Con several years back that she would never sell the rights to the Pern books without having control over the finished product. Something along the lines of not wanting to have her dragons attacking modern day Los Angeles....