This thread is scaring me, I just ordered two under quilts from Arrowhead! I have slept with a thermarest neo air, reflectix covered with a blanket and lastly a good old blue CCF mat and I have to say the CCF worked best for me. My only complaint about the CCF was that the friction between my sweatshirt and the pad made it hard to move around but that is the same thing that made it sit still in the hammock better than the thermarest. I think I chased the thermarest around all night to keep it under my legs.
My only problem is that I need to reduce the weight and bulk of my system so I can pack it on my bike.....with the pad I guess I will always have options to go to ground - but I hope I never spend another night in that bivvy!