I saw someone mention this in another thread, but it deserved it's own post. Land's End has a new 700 fill down jacket this year that looks like it might make a good insulating layer. It's called the SnowPack 700, packs into it's own pocket, and weighs 17oz for an xl, so less than a lb for a L. My email to cust. service got me the weight, they say they'll try to find out the fill weight from the manufacturing rep. I'll update if I get an answer.
Right now it's 100$, but earlier this week it was 80$ and I'm betting that after christmas we'll see them at 50-60. Looks like it might be a pretty good deal for discount shoppers/dirtbaggers.