Mine did not work for three days - it was about -15C. This prompted me to keep the bike inside the house overnight for a week or so - now it works perfect: but it is warmer.
The bike is an Alfine with fully enclosed cables from the shifter to the hub. Maybe there was some moisture in the housing - not sure.
This problem aside - I would still purchase the same bike if I need a bike. The ride is cheap enough that I do not worry about it at all and I generally ride about 300K per week.