Pete Doctor, director of our beloved Monsters Inc., has done it once again, with a riveting story boosted by humor and lifelike characters. In each of their films, Pixar decides/is forced to take on some problem or special effect that has never been done before in computer graphics, but is essential to the story. For instance, the hair in Monsters Inc., depth of field and cinematography in Wall-E, producing a full length feature film in Toy Story, and so on. The obstacle in Up was the thousands of balloons. A special team was selected, from what I've heard, that worked on them for over a year! Yes, only balloons.
But, just look how pretty the are and how precise the light and color distribution is through them!