If you are looking for a resource to learn ExtJS, this book is your guide. Its a wonderful book to say the least. The chapters are well organized and the teaching approach used by the author is really good for anyone learning ExtJS for the first time. The book starts from the absolute basics and moves on to advanced topics covering almost everything you'll need on a job.
The first six chapters cover the basics after which you can skip to any chapter you are interested in. The last two chapters teach you how to use ExtJS in a more manageable and efficient way in your application. The chapters on drag and drop were one of my favorites. The examples in the book make Ajax requests to extjsinaction.com to get a JSON response of random records which help you learn how to use ExtJS with data coming from an Ajax request without worrying about the server side code.
The only reason I've not given this book full 10 horseshoes is because of the errors in the book. You can easily find two to three errors in each chapter and there doesn't seem to be an errata as of now. The errors are not very severe so it can't be held too much against this wonderful book.
Disclosure: I received a copy of this book from the publisher in exchange for writing this review on behalf of CodeRanch.