I was talking to a few developers this week and they were telling me that they were really psyched about Flash Builder 4 but were waiting to upgrade. When I asked why, they explained that they were in the middle of Flex 3 projects and didn’t want to transition to the new Flex 4 SDK until they completed the project. I realized that in all of our excitement about Flex 4 and the new Spark component model, that we neglected to let everyone know that 80% of the new features in Flash Builder 4 can help you immediately with your Flex 3 application development. Andrew Shorten just posted a great new article in the Flex Developer Center explaining how to set up Flash Builder 4 so you can continue working on your Flex 3 projects with no disruption while taking advantage of the great new features. This article is a one-stop-shop to learn all things about migration, including both tool and SDK. James Ward also posted a short video where you can see Flash Builder 4 in action working on a Flex 3 project.
Flash Builder and Flex Product Marketing Manager