I bought the folding variety of the Thermarest pad, with the reflective side, and went camping with it over the weekend. (e.g. http://www.nationalathleticstore.com...egular_pad.htm)
Here are a few reactions:
Folds into a brick for easy, super-compact packing
Very warm. Absolutely no getting back-coldness, at least in the summertime.
Folding sections easily cover shoulders if you do the "cut it in half and turn the upper torso section sideways" thing.
"Egg crate" texture is comfy
Length of "R"egular size is excellent, ~6'.
The folds tend to fold back up inside the hammock when you're not laying on them, and require "smoothing out" sometimes. My hammock is double layer, so that was a little inconvenient to have to un-fold them.
Price: Almost $50 at the store near the mountain.
Were I to do it over again, I'd probably get the non-folding Thermarest.
"...the catenary, this marvelous graceful thing, this joy of physics, this perfect balance between rebellion and obedience, is God's own signature on earth. I think it pleases Him to see them raised.'' -- Mark Helprin, "Winter's Tale"