A fundamental difference between a two-wheel vehicle and a four-wheel one is that the two-wheeler uses friction to stay upright. Without enough friction, you will fall over in about as much time as it takes a bowling ball to fall off a table. I've taken a few of these falls and they tend to be very painful; in traffic they can be deadly.

Since I got studs I haven't fallen on ice, touch wood. I also find I can go up hills that cars can't make it up. Which brings up another point: in snow, even if you have studs, you also have to worry about cars losing control and hitting you. For me, this means keeping a larger than usual buffer -- keeping my distance from other vehicles, entering intersections cautiously, and riding "extra-vehicularly" to take my space on the road.

There is a lot of discussion on this topic in the commuting and winter forums.