To start here is a link for all you flex 3 developers who would like the free beta of Flash Builder 4 click here.

I follow Keith Peters blog and follow him on twitter and here is what he has to say about the migration from Flex 3 to Flash Builder.

I personally use Flash for all my development. I am trying to find a good reason to migrate to Flex other than the awesomeness of the code hitting. I actually use TextExpand and it is a great time saver. Check out this tut that highlights some ideas on how to use a text expander view video.

As far as the branding of Flash V. Flex I really don’t care as long as they find a way to make one stable platform. My cs4 constantly crashes, expecailly if I am developing anything that captures audio with flash.

Here is a rundown of Flash Builder 4 and Flash Catalyst on Lee Brimelow’s blog