I have a pair of asics novablast which I have been using for marathon training and after 1000 miles they feel fine. The details on the outsole rubber are beginning to wear away now. I weigh around 140lbs. I also have a pair of Reebok floatride energy and I could easily reach 2000 miles on those. The only reason I could throw them away would be if I got bored of them or they stank from wet trail running.