I have done approx 550 miles in my shoes. Having already purchased my next ones which are identical to the old ones, I put one of each foot and ran up the road to see how they felt. I thought the old ones wouldn't feel much different, but they did. The support and cushioning is much worn on the old ones, whilst the new felt like they had much more support.
I think that proves a point, or maybe I just run like a baby elephant and have been excessively heavy footed! :d
hmmmm, maybe it's about time to change my shoes... I'd heard of the 500mile rule, but never really taken much notice of it! Though maybe that's because up until now i've been a student and can't afford new shoes, heheh.