For the latest information on the next major release of Flex SDK and Flash Builder 4(codenamed “Gumbo”), check out the Flex 4 page on the Adobe Open Source site: http://opensource.adobe.com/wiki/display/flexsdk/Gumbo. The Flex 4 page includes the latest milestones, as well as links to the various public specifications. Also, you can check out the Flex 4 page on the Adobe Labs site at http://labs.adobe.com/technologies/gumbo/.
To download nightly builds of the Flex 4 SDK, check outhttp://opensource.adobe.com/wiki/display/flexsdk/Download+Flex+4.
For the latest Flex 4 documentation, check out http://livedocs.adobe.com/flex/gumbo/langref/ andhttp://livedocs.adobe.com/flex/gumbo/html/ (as well as some Flex 4 beta chapters at the bottom ofhttp://opensource.adobe.com/wiki/display/flexsdk/Gumbo).
If you think you’ve found a bug in the Flex SDK or in Flex Builder (any versions), you can file a bug in the public bug base athttp://bugs.adobe.com/flex/.
For a list of Flex 4 specific examples on this blog, check out http://blog.flexexamples.com/tag/gumbo/.