Here's a great article about this I read a while back (and one of the top reasons I don't like McChrystal).The reason a lot of the locals refuse to help the coalition forces is because they believe, correction: they KNOW, that long after the coalition is gone, the Taliban will still be there. So don't piss them off.
http://www.washingtonpost.com/wp-dyn/content/article/2010/03/13/AR2010031302464.html
It's a spin-off of the technique Marines used early in Vietnam of placing squads in villages and having them live with and protect the local population. It was widely regarded as a complete success, and then completely abandoned by the Army and General Westmoreland when they were given operational control. Westmoreland failed utterly, hopefully (and from what I've seen he is) Petraeus will be smart enough to know a good plan when he sees it.