My ride home yesterday was my first commute leg completely in the rain.
It wasn't much of a rain - a steady light shower - but it was enough that I wore my water-resistant workout suit pants and windbreaker. Added leather gloves, and nothing special under my helmet - I couldn't find my wool hat.

Turns out that, in the 50-ish or lower temps, that was perfect! Just a little cool, and with the cool rain on my head, I stayed just a little cool the whole ride. Didn't stink when I got home. Took it easy (careful, but not timid) the whole way. Only problem was a little trouble seeing through the raindrop-covered glasses.

I might still be cautious about riding to work in morning rains, but this was pretty pleasant, and of course, I had the whole MUP to myself!