WordPress 3.0, the thirteenth major release of WordPress and the culmination of half a year of work by 218 contributors, is now available for download (or upgrade within your dashboard). Major new features in this release include a sexy 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. (Twenty Ten theme shows all of that off.) 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

Check out this video tour below covering that and much more..

The update should not cause troubles for the majority of WordPress sites out there. Only plugin incompatibilities could result in problems, it is recommended to backup the blog before installing and to verify that the installed plugins are compatible with the new WordPress 3.0.