Now that school is out, I ride "The Dragon Lady" to work every day. That's an 11-mile round trip, rain or shine.
I have twin Mitsubishi engines on friction drive. I've been caught in the rain a few times. The rollers slipped like heck, but it's still a better ride than pedalling a regular bike in the rain.
When the roads are dry, I claim the lane and keep up with traffic, 40mph max speed.
When the roads are wet, I take a slower, safer route.