I think the difficulty of placing Dune in a category doesn't lie with the book, its lies with the category. If SF were well defined, it would be easy to assign literature to it or not. As SF is so loosely defined, we find it difficult. I've stopped trying to categorize the books I read - they are often fantastical, speculative or imaginative but I don't need to define them more than that. Whatever Dune is, its bloody good isn't it? This thread reminds me how great it is and makes we want to revisit it.