http://gotoandlearn.com/play?id=118

He demos and discusses the features with some detail, or you can read my cliffs notes version below:

• Major upgrades to video support in the IDE
  • Create cuepoints in the IDE
  • Play the video while its on the stage
  • Manipulate the video on the stage while its playing
  • More video player skins
  • Live video player skin switching
    
• Font Embedding Improvements
  • New Panel UI
  • Embedded fonts are globally managed through the new panel
    
• XFL Format
  • Replaces FLA format
  • FLA data is contained in multiple XML source files
  • Can version control XML files rather than binary FLAs
    
• SWF File size History is tracked
• Code Snippets included to implement simple functionality quickly
• Editor now has code hinting and completion for all imported classes (just like Flash Builder)
• Selecting an error in the Compiler Errors brings you to the source
• Tight integration for code editing with Flash Builder
• New brushes for Deco tool (Designers will love these)
• SWFObject2 used as default embedding method (just like Flash Builder)
• TLF (Text Layout Framework) gives you tons of options for doing awesome things with text
  • flow text between multiple TextFields, TextAreas
  • Multi-column text fields
  • Possibly automatically scrollable
  • Easier Internationalization, including right to left (Arabic) and vertical (Japanese)
  • Highlighting conforms to customized text flow
    

And a bonus!  Here is a walkthrough of how to export your ActionScript project as a native iPhone application!  http://gotoandlearn.com/play?id=116