We have just heard of release candidate 3 of WordPress 3.3 released yesterday. This was a last minute update by WordPress after working over tweaks and bug fixes according to a post on the website.
For now, WordPress has announced a release date for early next week, which means websites could now switch to version 3.3 before the Christmas break. If you're developing plugins or themes, you can test them on RC3 so that you can check any compatibility issues or breaks in code. These would be patched when the final release goes out early next week. Several posts on the development blog talk about WordPress 3.3.
For the UI part, even jQuery UI has been updated to the latest version. While WordPress 3.2 included jQuery 1.8.12, WordPress 3.3 will include jQuery UI 1.8.16. This would result in enhanced UI components for plugins that are not part of the core WordPress code.
Also in this release, there are some fixes with the wp-editor. Plugins can now access the WordPress editor from anywhere, including rendering the Visual/HTML tabs. Also, the links to upload files and displaying the media library can now be accessed by plugins.
Admin Bar API
The Admin Bar has been changed in WordPress 3.3. The added items in the Admin Bar API are not stored in a publicly accessible menu property. Instead, in a privately used property. According to WordPress, "if you were doing something like
$wp_admin_bar->menu->...,you won’t get anything back. The reason for this is that the internal structure has changed. Nodes are no longer internally stored in a tree. Now, they’re stored in a flat list, and the tree is bound together just before render. This makes the internal API much more stable, and allows us to provide plugin developers some nifty new tools. Even core only handles nodes using the same APIs developers use (mostly)."