I'd have to say winter riding is pretty awesome. Once you're properly prepared and the snow is suitable, it's a joy to ride. Generally, temperatures above 20 degrees were just about right. Anything less and some of my fingers would get cold. The coolest night I rode, at 13 degrees, was a little below my tolerance level. The studs work pretty well until the snow accumulation reaches 8-10 inches. Any more than that is still ridable, but the rear tire does a lot of spinning. In 4-5 inches of snow, conditions were perfect. I was able to ride about 70 miles in mostly open corn fields before hitting reserve on the 250XC. Fuel consumption increases quite a bit with higher snow accumulations, as the RPM's tend to rise while the rear tire searches for traction.
True ice conditions aren't completely ideal for the studs. The tires will still dance around on totally frozen water. For riding on lakes and ponds (which I haven't done), ice screw would be a better choice. The studs really start to work well with a few inches of snow. Handling is definitely affected by the studs, as they do add some unsprung weight to the wheels.
Snowmobiles are still a more comfortable choice for spending a day on the trails, and around here you can ride as far as you want. The snowmobile routes are linked up by the many local clubs who work with landowners and mark the trails with endless arrows, stop signs, orange diamonds, and many "danger" signs. The trails all pass through the local towns (with special attention given to the bars in those towns) and allow a snowmobile rider to fill up with gas and keep on riding. If you know where you're going, you can pick up the trail behind the Casey's store in Dakota, Illinois and ride all the way to Canada.
One of the dangers of riding a motorcycle across harvested cornfields that have been tilled in some fashion is the frozen dirt clods left behind. Any other season, the motorcycle's front suspension will handle these with ease. In the winter, however, the dirt clods are solid as rocks. Snow conceals many of these, and there were a few times when I was glad for my Scotts steering damper (and wondering if I'd find a flat spot on my rim).
One thing I would not recommend is riding a dirt bike on snowmobile trails. Some neighborly advice I received about this turned out to be wrong - we are generally not welcome. Even though the impact to the trails seems pretty marginal (compared to ATV's which are clearly prohibited, per trail signs), the snowmobile guys do all the work, and the trails are theirs. Visions of a snowbike conversion have crept into my head at various times, but a true snow machine is the way to go, if the intent is to ride the vast trail network that crisscrosses Northern Illinois and Wisconsin.