These following 2 quotes were mentioned on Leaky Cauldron. Just in case you guys didn't read them yet here they are :
There is one hint about the fourth Potter film. "Newell also said the costumes worn by the French girls in the films "drive the Hogwarts boys absolutely mad".
Oh god -_-' ..... I have nothing more about to say about this...
In the end, screenwriter Steve Kloves was among those who pressed for a single movie. "Steve wasn't sure what to do with the material he would have had to dispense with in order to make the first one ... coherent enough for a whole second film," says Newell.
So the challenge became how to make this film different enough to stand apart yet recognizably of a piece with the others. "What you do," says the helmer, "is you pack it with references and suggestions and so forth which, of course, you have taken from the book. So that a reader coming to the film goes, 'Oh, I see. I get it. They did it that way.' You're the guardian of the book, and at the same time, you have absolutely to be able to step off the books and say, 'We had better distill this.' Distillation is a very good word for it."
Sooooo...... More things will be cut lots of things will be cut. So they will probably mention things like "Oh yeah, I saw her during the ball" and skip the ball scene entirely....