Nike seems to be pretty popular! What features does it have? I don't know much about it but the Nike+ community looks awesome! I might buy it as my next watch.
I actually wrote a review on the Nike+ watch that's about 1,000 words long so if anyone wants a more detailed explanation, you can view my review here.
But basically it functions as a stopwatch, you can record heart rate as well, and in-run it tracks distance, time elapsed, "laps" (1 mile or whatever you want to set it as), HR, clock, average pace (overall for the run), and instant pace. You can also pause and continue very easily on it. The battery life is about 2 weeks for me, but I plug it into my computer everyday, which is recommended so that it updates satellites and other downloadable content.
The Nike+ Community isn't great - as in there is not much of a community. But plugging the watch into your computer uploads all of your run data and is put together nicely for you to view your progress on the Nike+ website. You can look at your week, month, year, etc. and view your longest run, fastest mile, 5K, 10K and your total distance. There are also "levels" in which you advance through and "points" that you earn for running longer and faster.
Overall it's been a really cool experience having the Nike+ watch - even if it's not the best in the trails.