I have the 0 degree version and it's been a good bag for the money. I remember picking it up on the REI garage. Only time I was disappointed with the performance was last year for 4th season elk. We were sleeping on cots/pads and I got cold every night once the stove burned out.
However, I did some camping in December the same year, had the stove going for 90% of the night (which could have been the difference), but was only on some tyvek/sleeping pad (which also could have been the difference), and was comfortable all night.
Not to derail the thread, but has anyone else had experience of being up on a cot with your pad, and being colder than just on the ground with your pad?
I have a 20* and have enjoyed it very much. It isn't anywhere near what I'd call a winter bag, but I have used it at elevation into September here in Alaska and with layers it kept me fairly toasty. For me, the bag being highly compressible was my number one priority. I stuff it in an Osprey longitudinal compression sack and it isn't much larger than a loaf of wonder bread.
That said, in my very real world experience, the DryDown tech is not a substitute for a synthetic sleeping bag.
During two very rainy hunts (caribou and sheep) in the bag got wet (then damp) and lost significant r-value.
Made for a few very chilly night when it's raining @ about 37 degrees. :/
(And yes, air underneath you will ALWAYS be colder than insulation)