Do you guys want to hear another theory about how Hodor got to be Hodor?
In Bran's visions, he is actually time travelling (as evidenced by Ned hearing him) and at some point he is going to warg into young Wylis to try to warn his family of the upcoming danger. But for some reason (warging into people is bad, or warging across time is bad) that is going to screw up Wylis' mind and he is going to turn into Hodor...maybe Bran says the word "Hodor" during the warging debacle.
So, Hodor helps Bran get to the tree where Bran learns to time travel, and while time traveling he wargs into Wylis and turns Wylis into Hodor, who later helps Bran get to the tree to learn to time travel?
Come on, guys, he just got kicked in the head by a horse...