I use an Outdoor Research Advanced Bivy on a regular basis. I like it alot. A major complaint with Bivy sacks is that they are clausterphobic and clammy. I have overcome these limitations by simply erecting a small canopy directly over my head using a poncho or an umbrella. A 1 meter square of bug netting is also a very nice addition to carry along. By leaving my face open to the air, bivy life is very enjoyable and much better, IMHO, than tent life!