In addition to the important user new features already mentioned in my previous post, WordPress 2.9 makes available a number of other new capabilities, like the following ones (excerpt from the related pages on wordpress.org):
■ Now there is the rel=canonical support for better SEO.
■ There is automatic database optimization support, which you can enable in your wp-config.php file by adding define(‘WP_ALLOW_REPAIR’, true);.
■ Themes can register “post thumbnails” which allow them to attach an image to the post, especially useful for magazine-style themes.
■ A new commentmeta table that allows arbitrary key/value pairs to be attached to comments, just like posts, so you can now expand greatly what you can do in the comment framework.
■ Custom post types have been upgraded with better API support so you can juggle more types than just post, page, and attachment. (More of this planned for 3.0.)
■ You can set custom theme directories, so a plugin can register a theme to be bundled with it or you can have multiple shared theme directories on your server.
■ TinyMCE WYSIWYG editing and Simplepie has been upgraded.
■ Sidebars can now have descriptions so it’s more obvious what and where they do what they do.
■ Specify category templates not just by ID, like before, but by slug, which will make it easier for theme developers to do custom things with categories — like post types!
■ Registration and profiles are now extensible to allow you to collect things more easily, like a user’s Twitter account or any other fields you can imagine.
■ The XML-RPC API has been extended to allow changing the user registration option. Some Atom API attachment issues have been fixed.
■ Create custom galleries with the new include and exclude attributes that allow you to pull attachments from any post, not just the current one.
■ When you’re editing files in the theme and plugin editors it remembers your location and takes you back to that line after you save.
■ The Press This bookmarklet has been improved and is faster than ever; give it a try for on-the-fly blogging from wherever you are on the internet.
■ Custom taxonomies are now included in the WXR export file and imported correctly.
■ Better hooks and filters for excerpts, smilies, HTTP requests, user profiles, author links, taxonomies, SSL support, tag clouds, query_posts and WP_Query
