Where the rubber meets the road you'll find all the salt, sand, rocks, metal shards, and glass that accumulates on the shoulder during winter. I put a new set of Michelin Krylion Carbon http://tinyurl.com/gyefq on my winter bike at the start of outdoor base training. When you are 35 miles from home and its 25 degrees, knowing that you've got some good rubber on your hoops brings confidence. Besides, you owe it to your fellow riders in the group.
Anyway, the Krylions, good rubber. Tonight I was inspecting the tires and I removed four sharp objects embedded in the rubber. The smooth tread is several millimeters thick. Money well spent.