CSS Design view: allows you to visually design UI components in the css file. updates components real-time
new absolute position controls
allows new constraint options, to attach to other controls, float....
"Move into style" button allows you to move component styles into a CSS stylesheet with a click.
Creating projects: made easier with new project wizard
allows you import web services using WSDL URI. Makes getting Web services very easy. Nice demo showing getting Dilbert daily. auto-generated classes!
making modules easier to implement: "modules are 'first class citizens'."
Digital Signatures for AIR apps. Signatures are enforced. you cannot distribute an unsigned AIR.