I wanted to post this as a "mini-review" of the following products that I just used for the first time: Warbonnet Blackbird 1.1 DL, Warbonnet Small Hex Tarp, Te-Wa Underquilt, and GoLite Ultra 20 Quilt (I've used the Golite before, but in much warmer weather).
Well, I finally spent my first night in a hammock...and in the same night experienced my first cold weather outing (15*). I did this in the backyard so I could adjust equipment (or jump ship) if necessary.
After fretting over what my "perfect" hammock set-up would be, I finally bought a WBBB 1.1 DL and the WB small hex tarp (the small tarp, in my opinion, offers plenty of coverage for the hammock - blowing snow did not get in when pitched tight).
For insulation, I wanted something that I would use mostly for 3 season hanging, but an occasional winter trip as well. I then talked to Te-Wa and bought one of his standard UQ's and paired it with a Ridge Rest pad for my first winter hang.
I have a Golite Ultra 20 top quilt, which many have said is not a true 20* cover. I started the night (when it was 20*) with a silk-weight baselayer, lightweight khaki pants, a cheap 100W fleece jacket, and wool socks over silk undersocks. I was also wearing a lightweight polyester (?) balaclava. Although my exposed face was cold, I was downright toasty and very comfortable. In fact, I unzipped my fleece and removed my wool socks.
As the night went on, it got down to 15* and the wind picked up. I began to get a little chilly, so I pulled out a silk bag liner and used that (this was much easier to deploy while inside the hammock than I had expected - I just put it under my quilt and pulled it on like a sock). Towards morning I was starting to get a little cold, but not so much so that I had to get out of bed. My breathing created condensation on top of my Golite Quilt, but it didn't soak through to the down.
Overall, this was a great first hang/first winter overnight for me, even if it was only in the backyard. I wouldn't, however, head out with the same gear if the weather was expected to get much below 15*, or if there was a chance I could get caught in much colder weather. But now I certainly feel comfortable sleeping in "freezing" temps and can adjust my gear as necessary.
And as far as the hammock goes - I can't see myself sleeping on the ground again! It really was that comfortable!
As a side note, my brother-in-law slept in two Big Agnes 40* bags (doubled up) on top of a Big Agnes insulated inflatable pad, inside a tent - he didn't even make it 1/2 way through the night before going inside.