I've been cycling through the winters for a few years now, and have yet to purchase a set of studded tires. I just flatten the knobbies on my mtn bike a bit, and off I go.
Having said that, I will add that I don't ride when the roads are covered in a thick sheet of ice. I ride when the road crews have cleared the road down to the pavement, or I ride on snow-covered trails.
If you use studded tires, under what conditions have you found that they are necessary?
Also, when you ride with studded tires on bare pavement, like when the road crews have cleared the road, doesn't the pavement wear the studs down? I would also think the studs would make the tires more slippy in situations when the road is slippery with frost (not ice). In those situations, the studs have nothing to grip into, and I wouldn't think there'd be much tread from the tires making contact with the road.