WordPress 3.0 Release Candidate 1 (RC1) is available for download. A “Release Candidate” comes after the beta release and before the final launch. Also, a “Release Candidate” has all features finished and all potential issues fixed. However, there are millions using WordPress with a wide variety of configurations and hosting setups, so it’s possible that they have missed something.
You can download the RC and test it out if you want, directly from wordpress.org
Some things to take in mind:
_Custom menus are finished! Yay!
_Multi-site is all set.
_There are a ton of changes, so plugin authors, please test your plugins now, so that if there is a compatibility issue, we can figure it out before the final release.
_Plugin and theme users are also encouraged to test things out. If you find problems, let your plugin/theme authors know so they can figure out the cause.
_The look of the WordPress admin has been lightened up a little bit, so you can focus more on your content.