There's an interesting interview on the Writers' Guild of America West site with Ted Elliott and Terry Rossio, writers of numerous hit films including Shrek and Pirates of the Caribbean [read the whole thing here]. Towards the end they talk about the emergence of a TV-style writers' room approach to developing film screenplays:
Terry Rossio: There's a trend, I want to call it the Pixar model. The WGA especially has promoted the idea of trying to have one writer, or limiting the number of writers on a movie, [but] you look at Pixar films, and they'll have four writers on a movie. They have a process up there of having multiple talents on a movie, almost like a think tank.
I think in the past there were these brilliant directors who held the whole movie in their head and brilliant writers who could conceive of a whole world full-blown. Maybe there aren't as many of those talents around, and in order to satisfy that need for blockbusters, we will be gravitating toward more of a team approach, when needed.
And there's obviously a difference between multiple rewrites down the line versus working as a team from the start...
Terry Rossio: There's a difference, but the effect is the same. It is actually legit to have a singular-vision movie that multiple writers worked on.
Ted Elliot: If writers end up in a situation of serial collaboration, there are two ways to do it: one at a time, without any interaction, which is the feature model, or to presume serial collaboration where needed from the start, which is the staff model of television.
Terry Rossio: And animation.
By the way, if you haven't already seen it, check out Ted and Terry's wonderful site about screenwriting. The section called Columns is particularly useful, both funny and full of great tips.