After putting out several films together, such as Monsters Inc., Toy Story, and most recently Finding Nemo (the most successful animated film ever), Pixar has announced that they will be severing ties with Disney, who distributed their works.
As usual, the argument was over money. Pixar wanted more of a share of the profits and a lower distribution fee becaus their movies were so successful. I can't say I blame them. Disney's going to shit these days.