I just saw Secret Window on blu-ray (looks great). I like this movie and it's a pretty good adaptation. The ending is changed from the book version (and that's OK) but I thought the characters were very true to the written story. There was a featurette in the special features section that the director talked about working with SK. He said that SK liked the script he wrote and made a couple of suggestions along the way. He said that SK was pretty easy to work with in that regard. SK doesn't want to interfere with what the director wants to do.

The novella is the best format to get a decent movie adaptation from. The 150 or so page count seems to be just right for a movie script.