I submitted the book to the iBookstore 48 hours ago, and am now waiting nervously for their approval, which can take between 2 days and 2 weeks, apparently. If it's not approved by Friday, I'll have a PDF version for sale here on this page. Once it goes live, I'll send a discount code to everyone who ordered the PDF and you can get a free copy of the iBooks version on the iBookstore. This means you'll be in the loop for future free updates of the book as well.
I'm also working frantically on a Kindle version, which I hope to submit sometime late tonight. I'll find out whether I can do the same discount code with Amazon as well. If so, I'll do the same PDF deal if the book isn't live on Friday; if not, the Kindle version will be available whenever it goes live.