I've worn these shoes for Ultra races (Headlands Hundred, Brazen Dirty Dozen 12 Hour), road marathons (Rome, San Francisco) and shorter events (legs of the Hood to Coast Relay) -- these shoes have never let me down. For the 100 mile event I did switch to a second pair 1/2 way through. Anyway, each pair was worn for just under 12 hours of running on fairly harsh terrain. For the 12 hour fixed time event I kept one pair on the whole time (over 100 k distance). The shoes are remarkable. I can train in the same shoes I race in. My only complaint is that the material used to make the Upper becomes brittle and then cracks and tears. This doesn't seem to effect the shoes performance but it doesn't exactly inspire confidence either. The upper cracks in the same place every time -- the crease just behind the toe box right under the point of the logo. Without the tears this would have been a 5 star review.