I've had several weeks of experience now using iTunes to manage some of my music. I've converted many additional CD's either in whole or in part to the AAC format. I've purchased a few more songs from the iTunes Store, and I've discovered a few "gotchas" that reduce iTunes' flexibility for what I want to do. But overall the experience is a good one and I am beginning to discover on my own the role that this type of software might play in an evolving "home media network."
But I have had to deal with the uneven quality of the indexing information for CD's that iTunes automatically down loads.
This is definitely an issue with classical music. I've found that "composer" and "artist" information are often switched or even wrong, and that individual movement names for symphnies or concertos may show up in the "performer" field.
I haven't looked for alternative sources, but I have been able to make certain, albeit manual changes. For example, the default browsing window in iTunes includes a column devoted to "artist." Clicking on "artist" shows all the "albums" and tracks where that artist name occurs -- assuming of course that the artist is spelled the same in all entries. I've been methodically going through and standardizing all the artist names (e.g., Sinatra, Frank) so that the sort order is correct.
All of which is to say, as a collection grows, the value of the index grows especially as the number of individual selections proliferates. Despite these issues, I am remarkably impressed by iTunes software and how easy it is to use, even in the Windows version I am forced to use (I am assuming it is a bit slicker in its native Mac format but I don't know that so sure).