i'm assuming you're talking about a question raised at WordCamp Chicago in June.
The book's contents all are applicable to WP 3.0 and future releases. There are new features in WP 3.0 (custom post types, for example) that obviously aren't covered. I believe my comment at the time was that we had the Wrox forums for discussion of the book's contents and that we'd comment on WP 3 issues/updates as appropriate.
I've been updated my WordCamp talk to make it WP 3.0 relevant, and have continued to share that content (as of WordCamp Boulder, July 11):
It is not our intention, nor is it Wiley/Wrox's usual publication process, to update sections or entire chapters online. Doing so without keeping the entire book internally consistent would be a disservice to readers.