The big feature in the new version of Flash is the ability to run hardware-accelerated 3D graphics inside the player. Together with some improvements of Flash's 2D capabilities, this should enable a 1,000 times faster rendering performance over Flash Player 10 and AIR 2. In layman's terms, this means console-quality games on all platforms mentioned above.
AIR 3 brings support for native extensions, as well as captive runtime, meaning the developers can automatically pack AIR 3 with their apps which will simplify the installation process.
Other new features of note are rental and subscription options for content publishers, content protection across all supported platforms (including mobile platforms) and HD video quality across platforms.
Check out a preview of the new features in Flash 11 as well as Air 3 in the video below.