In 3 whole winter of commuting, I've had the rear derailler freeze up on me a few times before. Once it was after a cold weekend. It took me a few minutes to realize that on Friday it has been raining hard. Saturday heavy freezing set in, and my rear cable froze before it dried out. After a few hours in my office, the bike defrosted and dried out. The other tires, I was riding through some wet sloppy snow and the whole unit was solidy encrusted on slush.

I've never had my shifters not work. I do use Poggies, and they keep cold and moisture away from my shifters and that may be helping.

Happy riding,
André