Forgot to mention that one of the most useful tools I have found in dealing with multiple copies of the same song in various formats, is too enable "KINDS" in the View options, of iTunes, especially useful sorting the main "MUSIC" library or individual columns for custom playlists.
To Set up select VIEW > VIEW OPTIONS > KIND> (2nd column 5 down). With KIND enabled to the sort fields, now clicking on KIND will organize any playlist into file types by clicking on "KIND" at the top of the column .aiff, MPEG audio file, Apple Lossless audio file, AAC audi file etc.
For quickly creating a separate mp3 list without creating another library, use a smart playlist with "KIND" as the single term to differentiate all mp3 files. For instance, use the term, 'kind" + "starts with" + "MPEG". Then check live updating to create a constantly updated MP3 song list.
For those with multiple formats in their iTunes library, it can become difficult to organize and keep track of songs. Changing from one Itunes Library compression method to another has been a lot of work. I recommend avoiding a lot of extra work by picking more wisely (than I apparently did) in the beginning, when setting up an iTunes library.
I recommend a dual .aiff library and mp3. This is the most flexible itunes library I can think of unless another lossless, fully compatible non- Apple standard can be found.
You can always re-record a bit perfect copy to ANY OTHER FORMAT LATER, from any lossless copy, without degrading the music. SO if you value that idea at least choose one lossless format.
As I have said before, I don't think the amount of time spent encoding and re-encoding and other limitations worth the space savings using Apple Lossless (you will only notice this re-encoding lag using Apple Lossless, AFAIK, on an older slower Mac or using Toast).
Committing to Apple lossless compression for ~20% space gain, isn't worth the trouble and deeper involvement with an Apple proprietary format, now that storage is so inexpensive. Inexpensive almost everywhere except on an Ipod.
An MP3 file can be made into discs that can be played universally in most DISC MEDIA PLAYERS and with higher bit rates quality is excellent. Apple AAC is just a pain to deal with, for what I feel is a very small benefit at the lower bit rates, which anyone who valued sound quality wouldn't choose for a compression standard the first place. A very small space gain for having to deal with an iPod/iTunes only format. Heck MP3 's plays fine in an ipod. Even Apple upgraded Library downloads from the abysmal 128 bit encryption. An embarrassment IMO.
The "Kind" view column is VERY useful in telling apart files that could contain nearly the same info except for format and file size. I use to use file size but it is much less precise.
The category "Kind" along with highlighting (CMD +A) similar itunes song files and then sorting by NAME again, displays ALTERNATING BLUE(highlighted) & WHITE text, for CD's that have an MP3 copy of the songs and solid white text indicating that those songs don't have another mp3 copy and need to be added to a bulk mp3 conversion, to run at slow times.
