Came into work thinking exactly that. Was 40 and raining; finally a chance to try out the ShowersPass jacket in its natural environment and with just a lightweight Smartwool layer underneath, it performed wonderfully. While the wool was a bit wet from sweat, I never felt hot and I was able to feel air circulating quite well inside the jacket. On the bottom, the 100 weight Polartec tights (Thanks, Icebike) with Endura shorts over 'em kept the legs toasty.

The Polartec truly makes me question the need for rain pants. They felt warm and got wet on the outside, but the piling on the inside remained dry. Combined with neoprene booties, I can certainly feel confident in this combo down into the freezing temps in moderate rain.