The duplicate song problem described by some users when adding to iTunes or cloning playlists has now been fixed in v4.2.

For iPod Access to decide that a song already exists in iTunes the ID3 tags of the songs must match. If the Song Name, Artist, Album, Track Number, duration, bitrate or file type is different on either the iPod or iTunes they will be considered 2 different songs. When using the "Add to iTunes" or "Clone Playlist" functions of iPod Access this criteria is used to determine if the songs already exist before the copy takes place. If the file does exist then a link to the song or video in the library will be used in the playlist. This should now work properly for all iPod, iPhone and iPod Touch users.

Special thanks to all the users who helped troubleshoot this issue.