I've heard that some of the civilian repros with Thinsulate are actually better than the military issued ones. Any thoughts on this? Has anyone out there used both and have some "on the ground" experience to share?

Also, not to throw a monkey wrench into anyone's plans, but there are down bags that are lighter than the two pound weight listed on the link that Blast provided. My 32F/0C Western Mountaineering bag weighs 19oz (1lbs, 3oz). It packs small. I unzip it and use it like a blanket if it's warm. Note that lightweight down bags are really expensive. For $21.97 you can't beat the poncho liner.