WordPress.org released versin 3.0 officially today. This version is a major breakthrough in this cms history and not only 
The thirteenth major release of WordPress, WP 3.0 is a result of six months of hard work by 218 contributors. The main features in this release include:
- new default theme clled Twenty Ten
- Theme developers can now easily implement custom background, headers, shortlinks, menus (without file editing), post types and taxonomies by using the API’s
- Merge of MU and WP, a really long awaited feature! (atleast for me!)
- New lighter interface
- 1217 bug fixes and feature enhancements
Click here for a tutorial on how to upgrade wordpress from 2.9.x to 3.0