Over at Flavorwire, they've put together a list of the
Ten Most Badly Bungled Classic Book to Film Adaptations. Their list includes such headdesk-worthy material as the Scarlet Letter (starring Demi Moore and an abused bathtub), Beowulf, and Tim Burton's Alice in Wonderland.
There's no question that these movies strayed more than a little from their source material. There are plenty of contendors for worst adaptation, though, and even more if you include comic books on that list. (Catwoman, anyone?)
What's your vote for worst book-to-movie ever?