Hi jags!
Yes! We emailed about this a couple years ago. Reflectix is what I use for my freezer-bag cozies so my food cooks (steeps, more like) in boiling water after I take it off the stove, saving precious (and weighty!) fuel. I've worked with it a lot for such things and in construction.
There are some real advantages. It is light, reflective, and does make a noticeable difference. I used some for an under-mat in the past. It is pretty quiet and not too crinky compared to other things. It is popular to a degree with the ultralight hiking crowd, and for good reason. Depending on where you get it, it can be amazingly inexpensive.
There are some problems in sleeping on it. As John mentioned, it is essentially aluminized bubble wrap. The bubbles can pop under concentrated body weight (leaning on an elbow or knees when getting up off the ground). It folds...but it also permanently creases (I use this to my advantage when making the cozies, taping the sides with adhesive-backed aluminum duct tape). It is bulky. For longevity, it is best carried rolled and then it is compact in one dimension but very long in the other. I also found to my dismay that under continued use, the aluminum rubs off and can transfer and then it oxidizes black, which can make what it transferred to (i.e. sleeping bag bottoms and tent floors) look un-good. Like most true air mattresses, it relies on trapped air for insulation, but there is really nothing else to make a thermal break against conductive heat loss. It works best as an under-mat or over-mat (I had better luck with the latter), layered with another sort of pad to add that bit of extra warmth. I liked the reflected heat...but the unbreathable surface was slick and I ended up with a wet back from condensation.
If you're really looking to go small (size of a soft-drinks can) and light, have you considered the Klymit Inertia X-Frame sleeping pad? It slips *inside* your sleeping bag so you can't roll off it, and the openings allow the insulation on the underside of your sleeping bag to loft up in between where otherwise it would be squashed by body weight. I've tried one. Not as warm in real cold as my Nemo Tuo dual-chambered self-inflating foam pads, but reasonably comfortable and really compact when packed. See:
http://www.rei.com/product/833850/klymit-inertia-x-frame-sleeping-padBest,
Dan.
