I won’t spoil the ending, but this article from Jon Negroni over at Mashable is worth a read. Negroni spent one year untangling the secret world hidden deep within Pixar films. This thesis originally appeared on his personal blog and quickly became a viral sensation. The author contends that every character in the Pixar films are all part of the same universe. And he proves it (with a stunning ending!).
Are the Pizza Planet trucks that can be seen in more than one Pixar film just Easter eggs? Or is there something more going on here? Read The Pixar Theory: Every Character Lives in the Same Universe and make up you own mind.