At this point there is one last thing I would try to do:
1 - Try un-checking the "Automatically send workout data to nikeplus.com" box on the Nike + iPod tab
2 - Click the "Apply" button on the bottom right corner of iTunes window
3 - Eject your iPod from iTunes
4 - Close iTunes
5 - Restart your computer
6 - Once it is turned back on open iTunes and reconnect your iPod
7 - Check "Automatically send workout data to nikeplus.com" box on the Nike + iPod tab
8 - Check www.nikeplus.com to see if it has updated
If the above doesn't work I would at this point contact Apple Care at 1-800-APL-CARE (1-800-275-2273). iPod customers receive 90 complimentary care as defined at the following website:
http://www.apple.com/support/complimentary/ (This is assuming you purchased your iPod in the last 90 days.)
You could also try calling the customer care at Nike.
I really hope this works out for you.