The first printing of the print version of our book is sold out. We are in the process of updating the book to add all the new stuff up to WordPress 2.9.1, as well as some new secret awesome bonus stuff. We've decided to hold off on the second printing until that is ready (next month). When it is done, everyone who has already purchased will of course be getting it as a free update.
If you are interested in only the PDF copy, you might as well buy it now since you'll get the update for free. If you are interested in the print copy, you'll have to wait until next month.