I go to work by bike making 6.000 km/year.
Conditions are: countryside environment, German snowy/icy winter (approx. 1..3 months).
Two years ago, my bicycle dealer pointed me to the "Schwalbe Marathon Winter" tire, which wears more than 200 carbide spikes on its surface (manufacturer's product page: http://tinyurl.com/5tcbvs3)
I tried it (if you buy only one, put it on the front wheel, as this is important for steering and all the little compensating steering movements to keep your balance - additionally, you can use your front brake to stop safely) and am now totally convinced: if you face snow and ice in winter, this is your choice.
Don't worry about melting days: when streets are clear, it runs with little friction loss. My daily ride is approx. 32 minutes, and I found no significant increase in time with the spiked tire on clear streets (although there is a noticable rolling noise).
This year, I was very lazy and left the Marathon winter mounted on the front wheel all summer long, and after thousands of km, there is still little wear-out of the hard metal carbide spikes (however, three of >200 have completely fallen out, which is still a good rate and acceptable for next winter).
The tire is not cheap (40..50 EUR per piece in Germany for the 28" / 622mm size), but if you cycle on snowy/icy winter on a regular basis, it's worth every penny!