Re: new/rented movies: DEVASTATOR!!!!!
I thought the same thing, but, like you said, I don't think the book ever took it that far during Ron's mental torture in that scene.I would have to wonder if that's for when Harry and Ron try to destroy the locket - the soul of Voldemort tries to convince Ron that Harry and Hermione have been hooking up since Ron left. I don't think the book is that explicit about it, but maybe they want to make it more unnerving for Ron in the movie.
Other than that, I can't imagine why Harry and Hermione would be naked together in any sort of love scene, unless they've drastically changed the story (which, I suppose, is entirely possible).