I live in San Francisco, so the winter isn't that bad (at least, not compared to the summer!). It can rain for extended periods of time and I don't ride in the rain (I don't work, which helps).
I have been thinking about getting a trainer that I can use in my garage for the extended periods (several days) when I can't get out and ride. I've made arrangements to get one but haven't used it yet. I also have a treadmill that I have used in the past just to get my heart rate up after several rainy days in a row.
I often plan a "training" tour for the fall (April) to motivate me to stay in "touring shape" during the rainy season and use that tour as my booster to full training shape for tours planned for later in the year.
Ray