For all you minimalists, I've found a way to get infinite miles on one pair of racing flats. For the most part, I run in my shoes until I have run the outsole completely through. Since I run in flats, this has become the only variable in determining when to buy new shoes. However, recently, I have discovered a way to prevent the outsoles from ever wearing away. I bought this product called "shoe goo," that is basically an epoxy-like glue used for shoe repair. I just put a thin layer over the areas of my shoe sole that tend to wear the hardest after each run. It takes about 24 hours to solidify, and this way, instead of wearing through the outsole, I just wear through the epoxy. If you do this after each run, you never have to worry about wear and tear.