I don't have a separate Winter bike, but I do have a dedicated commuter bike. I simply wouldn't want to wear out a nicer bike for commuter duty. On a really nice day I may ride my roadie or my Disc Trucker for fun, but rarely. Roads are bad too along my route. I ride with fat tires (26x2.0) and in Winter I just keep a set of wheels with studded tires so I can swap them if conditions become icy.