I have 3 ipod videos and an 80 gb classic that I put on about 6000 songs on through syncing of playlists. The ipods have identical music/playlists I periodically delete all the files on the ipods and resync to playlists. I have found that syncing behavior no longer works correctly unless I eject the ipod after I delete but before I sync. I think it used to work correctly, because I never used to eject after deleting (however, I also had fewer songs in the past).
If I eject the ipod after I delete all files, I will have an empty ipod. I then reconnect and it syncs fine.
However, if I delete all files and synch without ejecting in between, the sync misses about 150 files (various playlists) and I have to resync to get the remaining 150. I did a video and a classic with the eject process in between delete and sync and had no problem I did two video ipods without eject and both missed the 150 files (I believe they were the same files). I do not know whether or not those files were on the initial sync list or not. If need be I could delte another Ipod and test. Let me know if there is any value to this. P.S. The songs are missing without the 2nd resync. They were on the Ipod before the delete and on the first resync, the Ipod is short those songs and the Ipod stats are short the same 150 songs.