The Flex 4 SDK has some great new features but for existing Flex 3 apps upgrading might not yet be an option. Luckily Adobe’s professional tooling for Flex, now called Flash Builder 4, is abstracted from the underlying SDK. This means that you can take advantage of many of the new Flash Builder 4 features while still using the Flex 3 SDK. I recently recorded a screencast showing how to use Flash Builder 4 with Flex 3 projects. Check out “Moving projects from Flex Builder 3 to Flash Builder 4” by Andrew Shorten to see my screencast.