Its not something you would normally consider as an important design ethos, but the evolution of CD packaging has come a long way. Of course, most of the innovative designs have been in postmodern genres, but its credit that someone has finally compiled a book on all the various methods of packaging that have occurred over the years.
This may not appeal to most audiences, but if you're interested in graphic art and composition, then this is highly recommended. Of what little text their is, the author explains the pro's and con's of various style DigiPaks, the need for a change of thought when condensing design down to a smaller scale, and how we compare our feelings with this smaller, tangible product as opposed to the classic 12" cover. The net result throughout is that although the feeling of flicking through 12"s will never be replaced, the scope for DigiPak's is extremely wide.
The book is a nice size and, in my opinion, very well priced here on Amazon for the amount of content you get. I've also noted that their are various other books available in this line of products, so check them out too!