It depends on the tire, and the use.
Softer compound rubber will wear out faster (e.g. knobbies and dirt tires, cheap road tires) especially if used on surfaces which tear them up, like rocks or rough pavement.
Harder compounds will last longer, but at the sacrifice of cost and comfort (when compared to softer compounds.)
I've got over 1400 miles on my Schwalbes ($90/pair), but I used to burn through a $20 pair of tires every quarter back in college.
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"I feel like my world was classier before I found cyclocross."
- Mandi M.