Well, the worst part of working in a 20 degree (-7C) shop has to be holding on to your 20 degree tools. Anything with a metal handle (I'm looking at you, rebate plane) is right out. Plastic handles are a little better, warming up after a few minutes of sucking the heat out of your fingers.
Pennsylvania winters are not so severe, but it's been cold enough to keep me from getting much done. I made a short sanding board from a 24" sanding belt and some scrap wood. With the kerosine heater going, and the effort from sanding, I stayed warm enough to get most of the boat pretty smooth. I've been working mostly on the scarfs. I cleaned them up pretty well before gluing them to the hull, but they still needed a bit of work. They're looking pretty good now, but some of them have some dips that need to be filled. I'll have to wait for some warm weather to make an epoxy fairing compound.
I did have a couple warm nights that allowed me to fill the screw holes along the keelson where I screwed the garboard plank in place while the epoxy set up. I used straight epoxy where it wouldn't run out, and thickened the epoxy with wood flour where I needed to.
Aside from fairing around the scarfs, I need to finish planing along the backbone so it will be ready to receive the outer stem post, stern post and the deadwood. That can be done in the cold. I can also start making patterns for the posts and the deadwood. That ought to be enough to keep me going. Spring is not too far away.