Though it had occured to me once that Dean was Michael himself, that time during the 'Monster at the end of the book' episode, I can't remember the exact words, it was when Zachariah said that no one would dare hurt Chuck, that Michael himself would look after him, and yet Michael wasn't there but Dean WAS! Yup, that was when it kinda jumped at me, the thought that Dean was Michael, without Dean realizing it himself of course.