I'm pretty sure I haven't read this one, but I remember the floating island and the giant sea-snail made it into the movie. (In the movie, the islanders all spoke posh English and had names from Shakespeare, on account of a case of books once washed up on their shores or something. I don't know if the filmmakers made that up, or if it's from a different book. And I don't remember if the islanders were well-handled apart from that.)