How to sync two iPhones to the same Mac and to Nike+?
Humm, this is weird, mine does ok, but I never tried with both on iTunes... always one of a time.

I did found several forum discussions regarding the out of sync with Nike Plus, and this is from Aug 26th and already have 8 pages :o

it describes plenty of out of sync workouts (maybe it's an app bug)

http://forums.nike.com/thread.jspa?threadID=28016

probably is a good idea to post on Nike forum as well.