A few weeks ago, Adobe demonstrated a bunch of new features in Flash CS4 ("Diesel"), including inverse kinematics, animation curves and a new tweening model, 3D "postcards in space," advanced text, and encrypted video streams. Aran Balkin posted a video of the demo in Astro and Diesel sneak peeks at FITC Amsterdam - Updated.
Also, the Moockblog and Peter Elst have reported that Flash CS4 will be able to export and import a new source format based on XML called XFL:
"An XFL file is a .zip file that contains the source material for a Flash document. Within the .zip file resides an XML file describing the structure of the document and a folder with the document's assets (graphics, sounds, etc). The exact details of the XFL format are not yet available, but Richard assures me that Adobe intends to document them publicly, allowing third-party tools to import and export XFL." (via)
John Nack also noted various instances, including video, of sneak peaks of InDesign CS4's new Flash export features.