We saw the thread and wanted to add a little information. Thanks for trying out our software. Feedback like this is helpful as this is our first public beta release.
Duplicates are common, but this is usually due to iTunes making copies in other locations as part of sync, backup or the "Copy files to iTunes Music folder when adding to library" advanced preference. Most people dont notice this because only one copy shows up in your local library in iTunes. We share all files in the folders you designate, and if there are duplicates, we will display them.
If songs that you expect to be shared do not appear, it might be a few things. Simplify Media does not automatically share the contents of your iTunes library. Instead, it shares all the files in the folders you pick at install (default is your Music folder). Note it takes several minutes after install or a new connection for us to load the index of all the songs being shared. We filter out certain file types like wav, vorbis and flac. For songs purchased from the iTunes Music Store, we only display them if you are logged in with the same Simplify Media screen name on both machines.
Hope this helps. If it doesn't, or if you have any questions or suggestions, please email us at support at simplifymedia.
Bill Bradford, co-founder, Simplify Media