UPDATE: The on-line book was only up temporarily, to get comments from the artist. It's gone now. It'll be back up when the printed book is published.

Thanks for linking this, I was going through a previous edition. This has been an excellent resource for learning the Scheme language. It's been though learning scheme that I finally have come to understand recursion :)

I have been reading a lot about its power and ability to develop quickly in this language and am looking forward to learning it better :)

This book is a bit of a reference. If you want to learn from more entertaining books you should check out three books from another IU professor the Little Schemer, Seasoned Schemer, and when you want to move to logic programming the Reasoned Schemer.

What's new and special about this edition?

It covers R6RS.

Edit: More specifically, quoting from the book's site at MIT Press (http://mitpress.mit.edu/catalog/item/default.asp?ttype=2&...):

The fourth edition has been substantially revised and expanded to bring the content up to date with the current Scheme standard, the Revised6 Report on Scheme. All parts of the book were updated and three new chapters were added, covering the language's new library, exception handling, and record-definition features.

From a two second skim of the preface my guess is that it covers Revised^6.