If you don’t know them by now: Flex is basically Flash targeted at application development and offers for instance a free SDK besides an Eclipse-based IDE. AIR on the other hand is basically a toolkit for moving Flash applications to the desktop, offering some more sophisticated means to store data on the client in case the user is currently offline. That by itself is interesting, but if you combine it with Adobe’s goal to offer that runtime environment on Windows, MacOSX and Linux (the Linux version has not yet been released, but is currently in some kind of private pre-beta program), it is really exciting.
I really like the whole concept behind Flex and AIR, but most of all I like that both offer free SDKs. Correct me, if I’m wrong on this, but at least to me this is the only way to really get into ActionScript3-based stuff without purchasing for instance Flash MX 2004 or newer. And with the prospect of using it for online- as well as “semi-online” stuff not to mention the free educational license for the Flex Builder, I can only applaud Adobe to these two products.
Now I just hope, that I will find some time to really get into them beyond my current hacking-together of components I want to use ;-)