There was a good article in yesterday's Guardian by Frank Cottrell Boyce, which can be found here. As a little teaser, here's what he has to say about the three act structure...
All the manuals insist on a three-act structure. I think this is a useless model. It's static. All it really means is that your screenplay should have a beginning, middle and end. When you're shaping things, it's more useful to think about suspense. Suspense is the hidden energy that holds a story together.
I've been thinking about structure and pacing quite a lot recently, and this little article is helping me frame some of my thoughts in a wider context. I may well post some of this meandering old nonsense at a later date, but in the meantime, hop over to the article and have a gander.