This news is from TheServerSide.net.

MSDN has published a document outlining the major changes to the programming model and APIs used by developers working in ASP.NET between Beta 2 and the final RTM. Changes include disabled controls no longer raising events, the ability to exclude files from builds, and the removal of disk based caching.

The changes are grouped into several categories such as Migration and Compilation, Standards, Security, IDE and Project System, etc. Of significant note are changes in how derived classes are handled as well as how file names are generated.

Beta 2 Behavior
If a page is derived from another base page class and the base class contained control definitions or event handlers, when ASP.NET generated a page class dynamically, it was not able to see existing definitions in the base class and would potentially hide members in the base class.

RTM Behavior
The @ Page and @ Control directives now support the new attribute CodeFileBaseClass. These attribute allow you to specify the grandparent class for a page. The attribute values can be fully qualified. The compiler uses the information in this attribute during class generation to get a reference to the page's base type and to generate code that does not hide definitions in the base type.