We all know wordpress 3.0 beta is out and wordpress 3.0 will be out in May 2010. You can find the list of many of the enhancements and fixes.
wordpress 3.0 documentation for wordpress developers
All wordpress developers are looking for wordpress 3.0 documentation for development.
The WordPress 3.0 Codex is very good place to start working on wordpress 3.0
http://codex.wordpress.org/Version_3.0
Here I am giving the list of major changes of wordpress 3.0
* New menu management feature
* Improved custom post types (try the Custom Post Type UI plugin to see the possibilities)
* Improved custom taxonomies including hierarchical (category-style) support (again, try the Custom Post Type UI plugin to see the possibilities)
* New theme “Twenty Ten” is the only theme in the WordPress distribution, and is now designated the ‘fallback’ theme
* Improved child theme support; child theme use is highly encouraged and as described in the Child Themes article, very simple to accomplish
* The Default (Kubrick), and Classic themes, are no longer included in the WordPress distribution, but are available in the Theme repository
* Bulk theme update ability
* Standalone WordPress and WPMU code merged (Note: extra domain stuff remains plugin territory for this version)
* Configure a Network (multisite/WPMU) using wp-config.php file