At some point a few days after I installed Mac OS X Mountain Lion and the new Nike Connect software my Nike+Sports Watch GPS no longer wants to synch my runs. Watch works and charges fine.
This Facebook page tells me many others are having the same issue. I am hearing early models such as mine may be more susceptible to this issue.
I called Nike and after verifying there were no cracks around the USB connector and that trying to synch via another computer also didn't work they are sending me a new one.
Note that if you are on Mac OS X Mountain Lion and try to install the Nike Connect software you will need to go into your Security and Privacy Settings and chose General then unlock and chose "Anywhere" at Applications Download From as it seems Nike is not an "identified developer" according to Apple security.
The watch has been fantastic with software and features much improved from an initial very shaky start back in 2011 but it seems Nike didn't do their homework in upgrading Connect and making sure it worked with latest versions of Mac OS X.