well check and see what the tread looks like. are your sipes gone? is there enough tread there to evacuate water? (ie at least 1/4")
i got about 3 years out of my original blizzaks, and i am on season two of my new ones. if you drive on snow, and don't drive hard when you are on dry pavement you can really make them last. when it gets warm out and in the dry the compound really does melt away fast, especially at speeds and high lateral loads.