Adobe AIR 1.5 SDK (code named Cosmos) is now being included with the latest Flex 3 nightly builds. Aiming to bring the build process of Flex and AIR tighter together. There are some great things mentioned like the new JavaScript engine SquirrelFish, and fixes for the annoying opening of new browser windows.
Mike Chambers has a detailed post on the developments so check out his post.
TO get you hands on the nightly builds head on over to the Adobe Open Source site for Flex.