Makezine have made available an ebook early release of the "Getting Started with Raspberry Pi". As an early release eBook you get a copy straight away plus updates as they are made available, and finally a copy of the completed book. The ebook is available now for $11.99 in epub, pdf and Kindle Mobi formats. The dead tree version will be out around December for $14.99 plus postage from the US. It is published through O'Reilly, so its going to be good, and can be found here.