It an interesting book, and it shows that Java on OSX has a large enough user and developer base, for O'Reilly to bother publishing such a book. Wich can only be good for Java and Mac OSX.
However it seems that most of the book is made of of topics that could be found online especially at the O'Reilly
http://www.macdevcenter.com/pub/ct/45 web-site on Java. And with a little research you could find the rest online.
So I am sure to have a look once it comes in store, but O'Reilly will have to build some meat into it for me to purchase it.
But still good news.