The rating of Harry Potter and the Goblet of Fire is interesting. I am surprised that Warner Brothers didn't request the film be recut to achieve a more family-friendly PG, but I guess that since everybody was so pleased with the results of Prisoner of Azkaban that the powers that be are content to have the films grow up as the books do.
I fully expect there to be some sort of backlash about how dark the film is when it comes out, as there has been with both Chamber of Secrets and Prisoner of Azkaban. In both cases the hemming and hawing was seen pretty much for what it was, but this time around I think that there might be a more vehement case. While there were some disturbing images in both of the previous two Harry Potter features, the stakes will be raised very much in this installment. Harry's mythic passage to adulthood, which is at the core of the book series and now the films, involves dealing with an evil, evil man who is not softened to make him more palatable. An interesting essay on this can be found on suitboyskin's journal.
However, I was fully expecting the film series, because of the way in which the first two movies were adapted, to tone down the conflict somewhat in order to maintain as wide an audience as possible. One can make the case that only a severe misconception about the books and why they work would cause this, but Hollywood has some very strange ideas about how to adapt things. Nevertheless, this is a book series about growing up, and it seems that the films, like the books, are advancing in maturity as the characters do.
"Is it safe to masturbate as much as you two do?
I mean, Harry, you've already spent half of your inheritance on porn!"
If I had my guess, Prisoner of Azkaban is the last Harry Potter movie to be rated PG. Things take a decidedly darker turn in Order of the Pheonix, and while nothing really all that disturbing happens over the course of Half Blood Prince, the end would up the tension - in fact, I think that this is probably exactly what happened with Goblet of Fire.
Can one tell the quality of a film from its rating? Of course not. Star Wars Episode III was the first Star Wars feature to have a PG-13 rating and it still sucked. But given the material and how this film series has been evolving, it is significant.