Designer Features:
- Inverse Kinematics/Bones - More info (2)
- Tween Engine - More info
- Auto Tween
- Create Tween from the stage
- Auto Path Animation
- Tween Transformations
- Rescale Time
- View Keyframes by Properties (like After Effects)
- Live "on-stage" Video
- MAX 2007 Astro Sneak Peak - More info
- Advanced TextField Support
- 3D Effects
- Custom Blend Modes/Filters/Fills - Using Hydra
Developer Features:
- Aral Balkan - More info
- Typed Arrays
- 64 Bit Support
- Mobile Convergence
I'll keep this list updated as features are revealed. Be sure to check back. If I'm missing any known features please post in the comments.