Jabberwock has an interesting post up about Polanski’s film adaptation of Macbeth. This, besides Throne of Blood, is my favorite film adaptation of a Shakespeare play. Jabberwock’s entry discusses Polanski’s use of voiceovers instead of having the character speak their soliloquy outloud:
Polanski treats almost the entire soliloquy as a private contemplation, which is appropriate; these are deeply reflective words. Macbeth's lips move only once: when, clasping the seal that has been presented to him, he says the line "I am Thane of Cawdor“ almost as if to convince himself that all this is really happening, that his greatest hopes (and fears) are coming to pass. This is repeated in a later scene when a magical dagger seems to appear before his eyes “ he says "Come, let me clutch thee out loud but the rest of his lines are thought, not said.