I wore a Marmot softshell once because I forgot to bring my Sugoi (regular) shell to work. I have to admit, it kept me warm (microfleece lining) and windproof. The fit wasn't made for riding a bike, but it did reduce that bulky feeling. Doesn't breathe as well, but in cold temps, opening the zipper works fine.

Great, I just convinced myself to buy a softshell for biking, if the fit is right!