as long as you are Safari Books online subscriber - see it here.
Completely updated with XCode 3.x and Objective C 2.0. The screenshots even show the iPhone project templates, indicating the XCode 3.1 in some places. So far the only difference against reality I have found is not covering the XIB resource format (which is generated by default) and sticking with NIB. This blog entry has good explanation of the difference.
If you are fan of dead tree-ware books, the official publication date is May 2008, so expect it any day :-).
Strangely enough, as of May 4th, the author's web (The Big Nerd Ranch) does not really advertise its availability (yet)