I have my wifi-sync setup and working to my iphone4 and later today to my "new iPad". I've noticed that occasionally iTunes will decide to sync songs that are already on my iPhone. I sync my entire library. No music has changed or been added to the library. It, for some reason, will choose about 12-20 songs and sync them. They don't show up as duplicates in my iPhone, so I'm thinking the sync process deletes the existing and adds the new ones. I do run a windows home server and that server does duplicate the folder that my iTunes library is in. This duplication service ensures that my files are duplicated across at least two physical hard-drives as a redundancy. If iTunes is seeing an update to the filestamp time does it think it's a new addition to the library or something? Is there a way to filter this out?