The Adobe Flex 4 SDK Beta has been released. The release has been planned to align with that of Adobe Flex Flash Builder 4 Beta and Adobe Flash Catalyst. The latter is a new tool that has been much talked about in the community has a “no coding required” tag and is aimed at designers while the Flash Builder remains the developer’s tool.
For an overview of what is new in Flex 4, read Matt Chotin’s article. And to brace yourself when compiling your Flex 3 applications in Flex 4 Beta, read Joan Lafferty’s article. For instance, the Fx prefix has been dropped and namespaces have been adopted.
The architectural changes, and designer-friendly efforts have been public knowledge for nearly nine months now. Today those themes are: Design in mind, Developer productivity, and Framework evolution.
For an in-depth overview of Flex 4 read this excellent article by Sean Moore. Sean has exhaustively gone over possibly every new feature along with examples.
Remember, both the SDK and the Builder are beta versions and so use the public bug system where needed.