If you haven’t upgrade your wordpress to the latest version 3.0, you should do it now because the new version abounds in other new features while retaining the user-friendliness that has set WordPress apart from open-source alternatives Drupal and Joomla. It adds powerful features and additional complexity for those who go looking for them.
I have just upgraded all of my sites to the latest wp 3.0 version, very cool 
If you’re already running WordPress 2.7 or later, upgrading to 3.0 is as easy as clicking the “Update Automatically” button. But before you click on it, for just in case, make a full backup of your current WordPress files and MySQL database first.
The most dramatic change in WordPress 3.0 is the ability to host multiple sites – the fusing of WordPress Multi User (MU) and the core WordPress install. WordPress MU is a fork of WordPress that allows for one install to administer multiple (even millions) of blogs, it was separate from ‘regular’ WordPress before, but now with the wp 3.0, you’ll get the functionality of both from the same install. Just using one installation of WordPress 3.0, thousands of users can each have their own blogs under a common domain name. You can find the detail info in the article WordPress 3.0 Adds Better Customization.
Beside that, version 3.0 makes it easy to bring your old blog with you from another platform as well, which means the new version has the compatibility with the most common blogging services, including Blogger and LiveJournal, come pre-installed; others, such as Posterous and Vox.com, are just a click away.
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