Adobe Gumbo livedoc
http://livedocs.adobe.com/flex/gumbo/html/
Getting started with Adobe Flash Catalyst beta
http://www.adobe.com/devnet/flashcatalyst/articles/get_started_with_flash_catalyst.html
Building a data-centric application using Flash Catalyst beta and Flash Builder 4 beta
http://www.adobe.com/devnet/flashcatalyst/articles/building_datacentric_app_flashcast_flashbuilder.html
Differences between Flex 3 SDK and Flex 4 SDK beta
http://www.adobe.com/devnet/flex/articles/flex3and4_differences.html
What’s new in Flex 4 SDK beta
http://www.adobe.com/devnet/flex/articles/flex4sdk_whatsnew.html
What’s new in Flash Builder 4 beta
http://www.adobe.com/devnet/flex/articles/flex4builder_whatsnew.html
Effects in Adobe Flex 4 SDK beta – Part 1: Basic effects
http://www.adobe.com/devnet/flex/articles/flex4_effects_pt1.html