The new AIR beta has a lot of upgrades from the Alpha release, most importantly is the ability to drag/drop assets between AIR applications, the desktop, and other applications. Some other nice features include the ability to change the chrome of your desktop application depending on the platform you are delivering to, doing asynchronous file transfer, and file I/O support to read/write any file type to the desktop. Other tidbits included a comparison of AIR to WPF and SilverLight. AIR sits in a unique position between the desktop and the browser. You don’t have all the low-level hooks of WPF (baggage) and you are not living entirely in the browser. You have control to communicate with the desktop like any other application.
I think this gives you great strength to build an application that can be easily ported to other platforms (Linux, Mac, and Windows) with little or no effort. It also makes your technology road map a bit less complicated. You don’t have to depend on different technologies to port something from the Web to the desktop (or vice versa). The smart programmer will be able to take what they build in AIR or Flex (JS also) and move it between the two environments and share the majority of code between desktop and Web. That is a huge advantage over WPF and SilverLight.