Lorelle has put together a comprehensive guide of all the WordPress 2.3 news that is hitting the blogosphere.
It looks like there are an amazing number of people covering everything to do with the version coming soon.
In summary, tags will be built-in, and new Plugins and utilities for importing different Tag Plugins are being released. Changes to the database will break some WordPress Plugins that deal with tables for categories, so check the new WordPress 2.3 Plugin Compatibility List.
Check out Lorelle’s post for a great list of links to help you understand WordPress 2.3 better.