Little sceptical at first, but they really do let me run harder and longer. You can also feel the little extra "push" forward when you walk\run. Seems to be more noticeable when you are on harder surfaces (road or track would be best). I run mostly trail and gravel and have no issues unless the trail is extremely loose dirt or not very compacted as the zigs get sand\gravel in them, but it comes right out after a few paces. No size issues or foot pain, in fact they are working better than my old NB that I paid a lot more for.
Update 23 Jan 2012:  I scored the highest ever score on my US Air Force physical  fitness  test ever... went from a 89% to a 94%... smoked the run. Training with these shoes helped push me harder and built my leg strength.