I usually decorate my towns in their time. So when it hits winter, I'll put out poinsettias, snow Globes, Xmas trees and the festive candle while it still goes with my current decor.
Last year, I decorated my house with the ice set, the festive tree and festive wreath and snow bunnies. But that was before I had finalized my house decor. This year, I may still set out the snow bunnies, though. They go with my theme and I love snow bunnies!
As for the rest of my town, I've tried to landscape it so that it will look good in all seasons. So far, I've only swapped a few flowers around during the fall. Hopefully, everything will still look pretty good in the winter, but we'll see. I won't make any drastic changes, though, as I'm still working out the kinks in my landscaping and trying to get my town ready for a final dream address this coming spring/summer.
I do look forward to seeing some pretty snow-covered towns, though. I know a few people here have been working on Christmas themed towns.