Winter is my favorite season for bike commuting. Our winters are mild in NC with very little snow and ice (usually). It's easy to dress for the cold, with lows usually in 20s-40s, and I usually sweat very little. You do need a good light system, good tires, fenders and the right clothes to make it safe and comfortable. I would rather ride in the winter here than most summer days, which are usually very hot and humid.