I switch from road to mountain in the dark months here (when we also get most of our rain and fog, which means the air and road are usually damp every morning). I love my hardtail. Its like an urban assault vehicle (yes, I keep the knobbies on). I can hurdle curbs, I laugh at the potholes and rough roads, I can knock over the garbage cans and recycle bins that idiots put in the bike lane at ease - or mess up their piles of leaves (since they are too damn lazy to put them in the green waste bin) and generally do all sorts of mayhem.
(I only run through the leaves, though. Its fun in that Peanuts kind of way).
Plus, since I'm getting older, I like how much more balanced and secure the mountain bike feels, and, since mileage tends to drop in winter, the knobbies give me a much better workout for a 5 mile commute.
I'm even growing out my beard, I'm feeling SO manly.