another book i found regarding flex,

you might find this book usefull, it covers these areas:

• Tips on using Flex components
• How to validate and format data
• How to manage complex data
• Filtering, sorting and using cursors on data with collection classes
• How to consume Web Services using RPC components
• How to display data using list-based controls
• How to effectively compile and deploy Flex applications
• How to customize the look and feel of your applications
• How to make your applications more secure
• How to become more efficient in using the Flex Builder IDE
• Unique tricks such as calculating memory usage, making your Flex application into an active desktop, and customizing states
• How to use the ColdFusion Extensions for Flex Builder
• How to interface your Flex applications with server-side code written in PHP, Java, Rails, and ColdFusion
• Working with Flex in enterprise enviroment using the Flex Data Services, Java Remote Object and AMFPHP

Essential Techniques for Flex 2 and 3 Developers

recently i started to get more into flash,
as a flash / actionscript 2 programmer it interest me to get deeper into the flex / action script 3

here you can find a link for a downloadable pdf which can make your life easier understanding flex concepts.

Things you might learn from the book:

• The basics of doing design work using Flex Builder
• How to customize style and layout using CSS
• How to create and customize themes/skins for your applications
• How to bring design assets into Flex from Fireworks, Illustrator, and Photoshop
• How to effectively bring assets created in Flash into Flex
• How to spice up your design work with useful ActionScript 3.0 techniques
• Several invaluable Flex design techniques from multiple case studies

Flex for Designers