If you want to test out WordPress 2.8 Beta 1, you can download it here.On May xxth, 2009, WordPress Version 2.8, named for xxxxxxxxxxxxxxx, will be released to the public. For more information on this enhancement and bug-fix release, read the Development Blog and see the Changelog for 2.8.
You can view a list of all the new features here.
Since the release of WordPress 2.7, upgrading is very easy. You can use the automatic upgrade option via Tools/Upgrade Menu.