Joomla 3.1 has been released and is available for download at the Joomla website here.
The main feature of this release apart from a whole bunch of bug fixes, (all listed here), is the addition of Tags. There has been plenty written on this in the Joomla community, but if you'd like to read up on it take a look at "Tag - You Are It".
Joomla 3.0 to 3.1 is a one-click upgrade with backward compatibility and is not a migration, such as move from 1.5 or 2.5.