this has recently just popped up online, and has been doing the rounds on several film blogs i read. it's a fan theory that suggests that every pixar movie is related and exists within the same universe. it grasps at straws a little in places, and is more than a bit self-serving, but it's a very interesting and mind blowing read
http://jonnegroni.com/2013/07/11/the-pixar-theory/
http://jonnegroni.com/2013/07/11/the-pixar-theory/