Currently, the head seems to float over the ground rather than being attached to the player's body, you can see this very well while being in 3rd person.
Raise your weapon and move slowly, one will see that the neck is moving up and down but the head isn't moving together with the neck, which pretty much disables the head-bob effect aswell.

Related to:
http://feedback.arma3.com/view.php?id=14882