I don't make a habit of riding in the rain. when I do, I get soaked and can't pay attention as well as I ride.
Of course, there are times when I do go out while on errands. Also, when I'm doing extra-long rides, there isn't much choice. However, on one rainy day during the Trek Across Maine, it was so cold and wet that I ended up suffering from hypothermia. Sadly, I was brought in an ambulance to where everyone stopped for the night. Although a long, hot shower remedied the situation, I've learned a lesson ever since.