"The Lucid is my first down sleeping bag. I bought it after I decided I needed to pare down my packweight, and I have been very impressed with its performance. To start with, the Lucid weighs only 1 lb 12 oz, and it squashes down to the size of a Nalgene. When fully lofted, it reaches an impressive 5.5 - 6", though it is rated at 20°. I believe that rating to be conservative, as I've been warm in it down into the teens. The Pertex shell keeps water out, and the 800 fill power down keeps heat in. A very nice bag, all in all. I've heard it compared favorably to Western Mountaineering's Ultralite, but I can't confirm or deny, as I've never had a WM bag.
One problem: the zipper is notoriously snaggy. It doens't cause any damage to the bag, but it is an annoyance."