Sounds like a lot of great stuff in the new build (available free on Adobe Labs):

New Publishing and Optimization Features:

• Publish to web: Preview 5  has an option to specify if jQuery should be packaged with the composition, or downloaded from a CDN to produce lighter code and improve caching.
• Down-level browser support: Define a fallback state of a composition for non-HTML5 browsers like IE8 and below.
• Preloader improvements: Choose what gets shown during the preloader (before the framework, jQuery, or composition is loaded).

Emphasis on animation:

• Timeline: We made several significant improvements to the timeline that make composing animations much easier and faster, such as an easier to use Pin (formerly the Mark) and smarter playback behavior.
• On-stage tools: New clip and transform tools make it easier to manipulate objects and create animation effects.

Many other enhancements:

• Improved symbol functionality, stage editing options, the ability to swap images, more intuitive contextual menus, many bug fixes, and much more have been added to preview 5.