When I sync my iPad to my iMac, most of the time is taken up by Step 6 of 6: Syncing Genius Data to “Napier’s iPad”. It takes a few minutes and proceeds song by song through my music. What is this about? I hardly even listen to music on this, and the sync takes a huge amount of time relative to anything else syncing. It’s as though it’s copying all the songs over.
It’s data that tells iTunes what sort of music you listen to, so it can recommend music it thinks you’ll like. I’m not sure why it’s taking so long, let alone everytime you sync, but you can shut off the genius syncing in your iPad settings in iTunes, I believe.
Actually, it’s more about what other people who listen to your songs listen to and like, so it can tell you which songs go well together. Sometimes it does an amazing job at creating playlists, sometimes it’s very… average. It works better the more music you have and the more popular it is.