I haven't been following this thread... but based on the profile picture Gunson took during my consultation, I have pretty bad forward head posture.
If my neck is in good vertical posture, my jaw is almost completely absorbed into my neck. To avoid this, I've developed this forward head posture. Gunson has me down for almost 2 cm of advancement (lower jaw), so I'm hoping this corrects the problem (mostly a posture I've developed from being self-conscious of the neck chin look - which is SUCH a bad look).
In any case, I've been trying to work on my posture for the last 6 months or so. But, I imagine I have a long ways to go to get used to a normal posture.