I've been known to head out in the rain for a ride. I don't like getting the bikes totally trashed but at times it can be very exhilarating! Nice clean fresh air.
I've also headed out in the rain at night. At times I will take my MTB out just to be a bit more stable.
Even headed up GMR (to the shack) on a rainy forecast day looking for something different using the MTB. No rain, just some snow and hail!