I have a OR alpine bivy that I have used a few nights. It worked well, had temps in the low 30s with the windchill dropping it into the low 20s and rain throughout the night. Bivy really cut the wind and I woke up dry. I did find the clamshell opening hard to get out of without dragging my bag along with me. Also, at over 2lbs, it is one of the heavier bivies. Some of that weight can be saved by forgoing the pole.
I just bought a Bugaboo II that Bill was selling and can't wait to give it a try. It is almost half the weight of the OR, and seems to be very well constructed. It has a flexible wire sewn in to keep it off your face, saving the weight of a full pole. The opening seemed to be better designed as well with a T shaped zippered opening. The zipper is about neck level, meaning that the head of the bag should be trapped as you get out.
Overall, I am pleased with the OR, but think I may like the Bugaboo a bit more. We'll see once I get some forest time with it. I am planning on keeping both though, if that says anything.