I don't mean to shoot the whole theory down..... but I don't believe in dream guides.
Dream characters are a manifestation of our own imagination. So consciously and subconsciously, I believe you are your own dream guide.[/b]
Exactly, you are your own dream guide. Some parts of our mind fully understand what we are capable of in the dream world. I think of the dream guide character as a character that represents the part of our mind that most fully understands all the possibilities of the dream world, and appears to show the other parts of our mind, closer to the conscious level, what those possibilities are. Nothing new-ageish, just a reminder to ourselves of what we are capable of.

I think I met a dream guide once, in my first LD. I went with three other characters to try jumping to the top of a building. The first character jumped straight to the top and waited patiently for the rest of us, as we all hit lower parts of the building and slid back down to the sidewalk. It was as if one part of my mind knew what was possible, and was just waiting for the rest of my mind to accept what was possible.