Bartman,
I had seen this, but it refers to syncing libraries which implies that iTunes files are duplicated in the MC library.
I really don't want to duplicate 500GB of files!!!!!!
Am I missing something?
I use this tool, and both my iTunes library and MC library use the same .m4a files stored in the same physical location. I also use the 'duplication' method for my other file types (mp3, flac, ac3, dts, etc) using the sync to hand held method and converting non-mp3 files to mp3 in the process. I might re-consider duplicating the m4a files now that MC can tag them.
The main reasons for duplication are:
Convert file types to formats iTunes can handle.
Keep the two sets of files separated. Since MC is the 'master' library, you don't want iTunes doing something like changing tags or reorganizing your file locations and messing everything up just because someone changed a setting accidentally. HDD's are cheap vs the time it would take to clean up a mess made by iTunes.