I was trying to export my library from my iPod Touch, when I discovered not all tracks were exported. For some reason, Sharepod claims I have 1078 tracks in iTunes, while my iTunes Library only counts 998 tracks. I think this might be caused by me having many tracks with the same title. As of now, only 24 of 74 songs named "Allegro" have been exported, even though Sharepod claims they are all in the iTunes Library.
Sharepod does have duplicate detection when transferring music to iTunes, but the track would need to be an exact match for artist, album, and track name.
You can disable duplicate detection if you’d like by opening Sharepod preferences and going to the iTunes tab. Just uncheck the box to “detect” if items on the device exist in iTunes. Then, Sharepod will transfer all selected tracks to iTunes without checking whether the track already exists in iTunes.