If you have noticed the Auto Lock not working with iOS 6, there is a workaround.
The issue seems to be with the Assistive Touch; I use Assistive Touch on my iPhone to extend the life of the home button. When I use Assistive Touch to return me to my home screen I have noticed the Auto Lock does not work, the screen stays on.
There are a few workarounds:
1. My preferred option is to use Assistive Touch to return to the home screen and then (this is critical), place a finger on a part of the home screen and give the screen a wiggle or a swipe. The Auto Lock screen will then function as normal (Go ahead, test it out! – The important thing is, do not use the Assistive Touch to return to the home screen as your last action).
2. Alternatively, leave an app open. The Auto Lock will kick in as normal (again, test it out).
Be great if Apple could fix this bug.