Here's a grab-bag of links, with the first one being the most well-known on the Flex blogs. I still wanted to link to Joe Berkovitz's post on code coverage in AS3, because I'm excited to see this getting done (and someone making some interesting changes to the compiler). But I don't have much to add to the discussion. Go read Joe's blog for all the good details.
A new draft of ECMAScript 4 is out, and the mailing list is getting filled with interesting posts on the final proposals. Check out Insurrection, a thread which contains a thoughtful critique of ECMAScript 4.
I don't see anything interesting happening yet in the commit logs for Flex, but they're fun to watch again.
Nearly as much fun as the commit logs is seeing random new developments in all corners of the Flex world. I don't keep up with a good fraction of the blog posts on Flex anymore, so I'm sure I'm missing a lot of things like an Emacs mode for Flex.