A quick heads up on a new book covering Flex 4 which was authored by fellow Adobe community members (most are Adobe Community Professionals as well) Tariq Ahmed, Dan Orlando, John C. Bland II, and Joel Hooks.
The book is called Flex 4 in Action and constitutes an updated and revised edition to the previous Flex 3 book.

This book has received extremely positive reviews and whilst I have not yet read it myself I would wholeheartedly recommend it to anyone starting out with Flex or wishing to broaden their existing Flex 3 skills.

Tariq, the lead author, has this to say:
"The book assumes you know nothing of Flex. So it's optimal for software professionals looking to expand their skill set, an architect/technical manager conducting a deep evaluation of Flex in order to assess if Flex is a good fit, and teams looking to bring Flex into their technology stack. And if you're already working with Flex, and looking to go into Flex 4, the book covers all the concepts and features that were added to Flex 4.

The focus of the book is to provide a lot of coverage on the stuff you'd use all the time, vs. covering every possible topic under the sun and having to go shallow on the details. And even then, we came in at over 600 pages (and that's after we chopped stuff out).

For owners of Flex 3 In Action, we didn't want to just merely copy the previous book, but provide a lot of new content. That includes things new to Flex 4, but subjects such as MVC architecture that we didn't have space for in the prior book.

For example we took out the chapter on working with XML and made it available for free:

http://www.manning.com/ahmed2/ (look for bonus chapter 26)"

Readers describe it as 'Your one stop shop for everything you need to know about Flex', 'a Solid Start With Flex', 'Good reference guide' and 'Great book'.

Go and grab yourself a copy and hit the ground running.