WordPress 3.0, the thirteenth major release of WordPress is now available for download. Major new features in this release include a great new default theme called Twenty Ten. Theme developers have new APIs that allow them to easily implement custom backgrounds, headers, shortlinks, menus (no more file editing), post types, and taxonomies. Make sure to look at the new default Twenty Ten theme which shows off all of those things. Developers and network admins will appreciate the long-awaited merge of MU and WordPress, creating the new multi-site functionality which makes it possible to run one blog or ten million from the same installation.
And for even more information, check out the official WordPress Development Blog.