IGH kicks arse in the snow, but I find they feel a little stiff in very cold weather.

If you simply have to ride with a derailleur, whenever the drivetrain gets clogged up, stop, lift the bike about a foot off the ground, and slam it down on its tires to break loose the sticky slush. Another solution would be to use a stick you find on the side of the road to clean out the crevices and space between cogs.

I have a derailleur equipped winter bike this year, but (1) there has not been enough snow to really cause problems, and (2) I haven't actually ridden that much - just short errands around town, not to work yet as I always come up with some reason (too warm, meaning the road will be slushy, too cold, too much snow and road may not be plowed, etc). Last year I rode my Alfine 8 equipped bike and I love it more than my dog.

Edit: I read another poster on here a few weeks ago that he rides a good quality full susp. bike in the winter and that better quality components don't suffer as much as entry-level ones in the winter - well, the last time I had a derailleur-equipped bike it had Deore LX derailleurs and it was constantly freezing up. I don't know how people do it, but some do ride winter bikes with derailleurs and they don't clog up. Maybe they are just better riders than me and they can avoid every riding through slush.