Asking that question on an internet forum will generate a wide range of responses. Winter conditions vary in time and place, and every cyclist has different priorities and biases.
Speaking for myself, entering my 9th consecutive winter of transportational and recreational cycling, experimenting every day with various bike, gear, and clothing permutations, I have formed some distinct patterns, stuff that works for me, riding the streets of Minneapolis and Saint Paul and surrounding areas. For starters, let's talk bikes. I'll plan to get to clothing and various widgets later.
We always have one or two of these around the shop:
1. What's that for?
2. Doesn't it slow you down?
3. Can/do you ride that in the winter?
The answer to all of the above is "probably".
The "early adopters" in the lifespan of commercially available fat-tire bikes like the Pugsley were people who were either eccentric or into riding on snowy trails or both. Of course, the definition of "snowy trail" varies, but these fat tires generally work best when the trail is well-packed and/or groomed, such as is the case of many snowmobile trails. They don't "float" over fresh powder snow (unless it's really shallow), nor do they have much advantage, by and large, on snow-covered city streets, regardless of whether the snow in the streets has been plowed, packed down by the pressure of thousands of car tires, or turned into rutted, salty, icy, oatmeal/pie-dough, which, in my experience is an archetypal Minneapolis winter condition on low-traffic side streets.
Not too long ago, some of the people who make and sell fat-tire bikes stopped calling them "snow bikes", and actively promoted the idea that these bikes are better regarded as "fat bikes", which are good for lots of interesting types of riding, but are not necessarily the best thing for every conceivable version of snow. After all, this would likely be a fun bike in lots of places that never get snow, or for riders who have no interest in riding the Arrowhead 135. The insistence on product categorization is a double-edged sword - create a purpose to sell the product, while not alienating too many potential customers in the process of defining the niche.
In short, fat bikes are a ton of fun, and they have a lot of practical applications. But don't make the mistake of thinking you need to get one before you can ride during the winter, or the corollary mistake of thinking that riding in winter is the only rationale for owning and riding a fat bike.
I've ridden various winter steeds in the past 8 winters, and this bike is the culmination of my winter bike tinkering up to this point:
Fixed-gear is a version of single-speed without the freewheeling mechanism. In practice, this means that fixed-gear riders can't stop pedaling and coast - the pedals are always moving, except when stopped or skidding. Sometimes I tell people this, and they wrinkle up their noses and ask, "why would you want that?" Of course, if you have to ask, maybe you don't want that, which is fine. Maybe you don't want a freewheeling single-speed either, which is also fine. But if you did want all the great things about the Cross-check, but with the reduced-maintenance of a fixed-gear or single-speed, you'd have to either buy the multi-speed Cross-check and modify it, or buy a frameset and build up your single-speed from scratch. Either way, the costs added up to more than many wanted to spend. Surly came to the rescue this Fall with the new Cross-check single-speed complete bike. We just received one today. The color is a swanky deep gray-blue, and the price of $999 makes it a bargain. If you're looking for a stock bike for urban commuting this winter, this is, by my standards, the best you can do.