Like all Pixar films, Toy Story 3 features a short film before the feature. The new short is called Day & Night. The short is hard to describe -- it's the first Pixar film to include any hand-drawn 2D animation, though in this case there are two 2D characters with 3D worlds inside them. There's a visual explanation in the clip below:
Have you seen Day & Night? What did you think? I haven't seen the whole thing yet, and frankly the clips above seem a little baffling, though I've heard rave reviews so far.