I just beat my personal record for winter biking: Last winter the coldest I rode to work (20km each way) was -5°C. About a month ago I rode 2 or 3 days with -8°C, while yesterday evening it was -10°C when I returned home. This morning I saw -13.5°C on the thermometer and still took the bike, but cheated - I took the train for 2/3 of the way. The return was on bike, but it was "only" -7°C, so I even broke a sweat
Last year I read an interview in which a doctor gave tips on biking in cold weather. One of them was that biking for more than an hour in temperatures below -10°C can be a health hazard.
The bike is all white from the salt, unfortunately the road maintenance crew have no mercy
In some places they poured so much, that there wasn't enough snow to melt and dissolve the salt...
One of the things I've noticed while commuting for the last 18 months is that my average speed is proportional to the temperature - the colder it gets the slower I go. For example, my average speed for the whole week (200km) is 22-23 km/h in summer (my best week was 25 km/h!), which drops to 17-18 km/h in the winter. I would think that colder tire rubber has lower rolling resistance, but then cold air is denser, increasing drag. More likely my body is using more energy to keep warm, this would explain why I am more tired at the end of the trip, even though I am going slower.