They end up as a fairly small package when used with a compression sack, and look pretty good for the price you can buy them for. I must admit, once it drops under 50, I have high end down bags that do a great job for little weight/space penalties.
I watched a you tube of a patrol bag in use. I was shown the 4 part system by a military friend, but haven't used it. Used with a woobie, I would guess under 40 is getting possible. Not bad for a cheap modular, relatively lightweight sleep system. Before my good friend that is very involved in logistics/supply took his full time commission and started doing his equipment testing in Afghanistan and Iraq, he owned a backpacking store in Vt. (My wholesale priced toy store!) We often laugh about the difference in philosophy between outdoor companies and the military. The military could care less about comfort. Being kept alive is all the comfort a soldier needs. We're going to do a trip together early this summer, til then I won't see one in use up close.