When I heard about it I was as surprised as you may be, reading the title of the post. Film making in Unity? Isn't Unity used for making Games.... Well, Its true Game Engines have been taking part in making Films too. One such example was the movie 'The Jungle book' where Disney used Unity for Faster Previews and real-time rendering. You can refer to this article foe more: http://www.icgmagazine.com/web/bare-necessities/
Surprised huh? Yes Unity was used in making of Disney's Jungle book, Unity is free and has tools that can deliver realtime fx & rendering. One more example I recently read about was this French Animation Show called 'Mr.Carton' Which is also the world's first cartoon series made using UNITY. This is fully done using Cameras, Lighting, Set building was all done in Unity.
Here is an article on Unity3d's blog
I am sure that film making using Game engines is gonna be more common in near future. Hope you liked the article, share it to spread the word.