I've found it to be accurate most of the time... Ive run with it since May and have compared it on many occasions with my buddy's Garmin 405. 98% of the time, the discrepancy between the two on a 9 mile run is no more than a tenth of a mile.
I've noticed, the Nike links to satellites wayyy slower than Garmin... Which can be helped by constant updates with the computer, but that can get annoying.
One thing I've noticed is that when you stop the Nike, and then start it again, it doesn't start counting mileage right away... Like it loses its satellite connection when you pause it and reconnects when you start and it's super annoying because we've noticed on runs that require pausing the watch 5+ times, the Nike could be half a mile off after only a 5 mile run because you run a tenth after starting it before it links and starts ticking mileage again...
Also, the Nike "split" times by hitting the screen absolutely suck...
I'm ok with the Nike and won't get rid of it... But if it breaks, I've getting a Garmin