How many miles do you folks put on a pair of sneaks before you retire them from running duty?

The "industry" used to recommend 300 miles a few years back, but when I ran in Newtons (for about six years), I was getting about 450 miles on a pair before retiring them. 

Most recently, having switched to Altras, I have put 400 miles on a pair of Escalantes. (Incidentally, my favorite road-shoe yet.) The bottoms have worn well (but I'm wondering about the cushion lately). $00 seems pretty respectable.

But what say ye? When do you decide to relieve your running shoes from athletic duty?

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