As May 28 2010, WordPress release WordPress 3.0 release candidate 1 (RC1). This release have all features finished, all bugs squashed, and all potential issues addressed. But please keep in mind, this only the release candidate, don’t install or upgrade your live site with this version, unless you know what you are doing.
Things you need to know with this release candidate:
1. Custom menus are finished!
2. Multi-site is all set.
3. The look of the WordPress admin has been lightened up.
4. There are a ton of changes, so all your plugins need to be tested for compatibility issue.
5. Themes also need to be tested for the compatibility issue.
6. And a couple of known issue. Please read it carefully here.
You can read their announcement here.
Download and try WordPress Release Candidate 1.