iPad: The Missing Manual should be available to purchase and download later this week.
Early access to O'Reilly ebooks is one of the many fringe benefits of my job. I've been enjoying a PDF version of this one since last Friday. Author J.D. Biersdorfer has done a terrific job providing all the iPad info you need; this product truly is "the book that should have been in the box"!
Btw, here's a tip of my own...not something from the book but rather something I've learned while reading the book... The ePub version of this Missing Manual isn't quite ready yet, so I've been reading the PDF version on my iPad. I didn't purchase a separate PDF reader app though. I've been using the GoodReader iPad app for awhile now, mostly for Google Docs access. GoodReader also lets you read PDF files and it's been a great solution while I wait for the ePub file, which I'll be able to load directly in my iBooks library. If you use Google Docs or read lots of PDFs it's hard to go wrong with the 99-cent GoodReader app. Highly recommended.