I haven't toured in the winter, but I bike commute all winter long. Living in the South (NC) helps as we don't get much snow and lowest temperatures are generally in the teens. The biggest hurdle to winter touring here would be all of the extra clothes and heavier gear (eg, sleeping bag) you would have to carry. It would take up a lot of space and add more weight. However, strictly from a comfort standpoint, I enjoy commuting more in winter than I do in summer. It is easier to dress for cold weather than hot, humid weather.

I am generally commuting to work in the coldest part of the day, so I have to closely monitor the weather. Sometimes I have to drive because the roads are just too risky for cycling due to ice, sleet, freezing, snow -- particularly at 6 am. If touring, you generally would be able to leave later and usually avoid icy conditions. I have often commuted to work in mornings when the temperatures were in the teens and low 20s at 6 am, but warmed up to the 40s by 9-10 am.