Air is Adobe's initial foray into desktop development. As you might imagine, Air is essentially Flash for the desktop. I'm not impressed at all. Air gives you 3 development options: Flash, Flex, or HTML.
Flash is primarily used by designers for ads, video playback, and small games -- notably, no "real" development. Seriously, what intelligent person is going to develop a significantly sized app with ActionScript?
Flex seems to be the preferred method for creating Flash and does so using a proprietary markup syntax. Flex still uses ActionScript, tho, which begs the question: who in their right mind would use this for anything more than a trivial app?
If I was Adobe, I'd latch onto a more powerful platform, like Java -- I'd say .NET, but we all know that won't happen. I don't see Air going too far due to the lack of strong underpinnings. Then again, I have been surprised at the apps that have picked up on it. Perhaps HTML support is more about migration strategy than a quality development platform. I'm definitely interested in seeing where this goes. With Silverlight 2.0 on its tails, Adobe is under the gun to make some serious movement in this arena.