So here is what I did, (keep in mind that the project I have it on I only had just the player and a wall and some terrain, there was not a lot of computation going on). I am using unity, who's mechanim system pretty much took care of the IK and the animation and the movement, so I just strapped the camera to the player's head and excluded the head and jaw bone from animation and made it controlled by the mouse. It worked fine because then in first person the collisions and movement felt natural. The one thing that I did notice sucked was that the head bone was influenced by the torso so when he ran and lent forward the camera would lean forward as well. And the only other problem I see is that if you had other parts of the PC's face where the rendered side could be seen by the camera (eyes, brow, tenticles, horns if not human) then the head needs to be a separate part and set not to render. You can even influence the character arms to hold a weapon where you are looking. I have had a fair amount of success in a limited test field. I'm not sure how much impact it would have doing this way in a scene where the is a lot of rendering and calculating but it is worth a shot.