I just got my copies of "Extending Flash MX 2004", and what a great book it is! Though I might be a bit biased on this, I do honestly think it is one of the - if not the - best Flash reference book(s) around.
Kudos to the authors Keith Peters and Todd Yard (thanks for the kind words in the acknowledgements guys), Guy Watson aka FlashGuru for his foreword to the book and ofcourse Steve Rycroft for doing a great job with this project!
Inspirational stuff, I'm sure we'll be seeing more JSFL extensions coming out to the public soon. If you're interested in discussing Flash MX 2004 Extensibility further, you might want to check out the ExtendFlash mailinglist kindly hosted by Guy Watson or the forums on the books website (http://www.flashextensibility.com).