I also experienced problems once with my camera’s mirror, while taking photos for a couple of hours at -20 degrees. (It’s hard to stop taking photos when there are awesome northern lights up in the sky!) Afterwards it seemed fine as well. One of my batteries had problems afterwards, though.

One thing which is important when taking photos: good vs. flexible protection for your hands. I also have two layers of gloves; one light with good grip (I used to have some mountaineering gloves, which were perfect, but then I lost one of them and couldn’t find a good replacement), and some big warm ones where my hands fit in with already one layer of gloves on 😉

I also like to have a balaclava on me when taking photos for hours at these temperatures. Also looks stupid, but when you’re out alone in the night in the wilderness nobody cares 😉

Another thing which looks stupid but helps a lot: if you use a metal tripod, add some layers of duct tape to places where you want to handle it. And don’t take off all layers of gloves when doing so. Otherwise your fingers might get stuck 🙂