[AS 3] How to increase performance?

Im making an interface which contains alot of buttons and instances, but i get problems with CPU running at 30-50% when i move the mouse around in the movie. I have removed all mouseevents from the clips, and it didnt help anything. I have approx 900 clips in the scene, using about 35MB of memory. Since the clips are mostly buttons, the clips are mostly duplicates of together 9 sourceclips. I also use int all over and not Number.

Its programmed in AS 3.0 classes and compiled with mxmlc.exe.

So what i wonder is what stuff should i look out for and what tips and tricks is there to avoid
heavy load when the mouse is moved over the movie.