I'll probably do a better write up on this later, but just wanted to drop a quick note about my experience running a marathon with th Apple Watch. I ran with a 42mm sport paired to my 5s on one wrist and my trusty Garmin 305 on the other. The distance measured was exactly the same between the two, coming in at 26.42. Which was pretty good considering I didn't run the apex the whole race. I talked to a guy using a Garmin Fenix who said he was on the line the whole time and his watch measured 27.05. The watch performed great the whole time and was able to show my pace even when my Garmin couldn't when satellite reception was blocked downtown. Battery life was better than I expected. I turned it on at 6:30am then ran just over 4 hours with the watch set on open goal outdoor run and the watch didn't die until 3:30pm and that was after I used it for directions home (I didn't put it into reserve power mode). I would absolutely use it again and would choose it over the 305.