My coldest ride so far this year has been -36 degrees Celsius not counting windchill. Just for reference, you Americans, -40C=-40F. Riding in temperatures like this certainly has its challanges, ski goggles, an insulated snowboard helmet plus mask (or two) make things much more tolerable.
I've also switched to a fixed gear drive train this year. There is nothing worse than solidified grease in a non-engaging freehub. Low temp or liquid grease in the hubs also makes things roll a little smoother in the cold.
I've actually had some really enjoyable sub-30 commutes. The snow is dense and fast rolling as smooth pavement and there's little traffic because nobody's cars will start!