In general, I find that motorists treat cyclists better in winter than in summer. I seldom get any grief from motorists for this. Watch it around stop signs. Air headed motorists are usually quite surprised to find that the darned thing doesn't want to stop all that well and they will come sliding right through. Generally watch intersections very carefully in winter.
Flats are also less frequent in the winter.
There are fewer drunks riding around throwing bottles out of car windows, and more snow plows flinging road debris off of the roadway. In some parts, the only time of year the bike lanes get maintained is winter when they are plowed. Traction Just because a portion of the road is clear of snow does not mean it provides good traction. Often the wheel tracks get a glaze over them due to melting of ice and snow as the cars drive over it, followed by freezing again. This yields a thin layer of nearly invisible black ice.