After writing the post on a disappointing celluloid version of an appreciated book ("A plea to the authors"), I tried to classify my books in Library thing (www.librarything.com) based on whether a movie has been made on them. I was surprised to find that out of 172 books in my library, atleast 52 have been made into movies - and I was hardly aware of any of them barring a handful! Almost every classic has been filmed, and a lot of them have poor ratings on IMDB.
That brings me back to the same thought - why do some of the brilliant books end up being unimpressive on screen? Is it a matter of expectation mismatch or are most good books more an interplay of words and thoughts, better expressed in pen than dialogues, and hence unfit for celluloid consumption?