Every time I sync my iPod (Touch 2G), there are about 20 or 30 songs that iTunes insists on syncing. I usually sync just to get a couple of updated podcasts, but have to wait while it needlessly syncs the songs. The songs themselves seem to be fine, as I've listened to some just before it thought they needed to be synced. Nothing is changing on the files themselves - I haven't been updating any tags or album art or anything. Any idea why it thinks these same songs need to be synced every time, and how I can tell it otherwise?
If you played a song once on your iPod and three times on your computer since the last sync the data related to that file is going to be different. iTunes will then update the play count information on both your iPod and computer with the correct information (add 3 plays to the iPod, 1 play to the computer). This doesn't mean it's updating the song file itself, just the database information related to that file.