IMHO I feel that movies will never replace books. I'm an avid reader and every movie adaptation I've ever seen cut out too much of the plot from the book. If I hadn't read PoA first, I know I would have gotten lost if I had only watched the film.
I had to fill in all the missed details because I was the only ne who read the book frm my family. Finally managed to get my husband to read GoF and OOTP, and HPB (when it comes out) so that he can get all the info from the books now.