1. UpdateProgress control. The UpdateProgress control is now part of the supported core.
  2. Client-side localization. Client scripts can now automatically retrieve localized resources from the server, making it possible to create locale- and region-aware Web interfaces.
  3. Simplified event binding API. Added functionality for binding and detaching multiple event handlers to a DOM element with a simple function call, which reduces the amount of script and helps prevent memory leaks.
  4. Client control CSS-based style support. Added functionality for using script to add, remove, and toggle CSS class associations on client controls.
  5. Performance and stability improvements
    • Control designers are now installed in a separate assembly for less server overhead at runtime.
    • The ScriptManager control has support for configuring a timeout and for detecting scripts that time out when loading.
    • Script components can now register for dispose semantics with the ScriptManager control to avoid memory leaks
  6. Debugging and tracing improvements. Better support for identifying and diagnosing issues during development and deployment.

This Beta release is a preview of the fully supported version of ASP.NET AJAX that is scheduled for release near year-end. Beginning with this Beta release, the Microsoft AJAX Library is also available in an easy-to-install standalone package for development on non-Windows systems. (ASP.Net)

Download it here.