Just 2 hours ago Apple announced that their latest version of the Macintosh OS X v1.4 (aka "Tiger") will be available April 29, 18:00 PST at a retail price of USD129.00.
Apple is planing events at most of its Apple Stores around the world for the launch.
You can pre-order it from Apple's Online Stores worldwide.
The most significant enhancement in this version of the Mac OS X is "Spotlight", which I believe every Mac and non-Mac users will find it useful. Simply put it, Spotlight allows you to find anything on your Mac without worry about where or in what format the information are stored.
To get people started with using Spotlight, Apple had included the Spotlight functionalities into the new Mail, Address Book, System Preferences and Finder. The best part is that the "Spotlight" technology is built into the heart of the new Mac OS X and not a "bolted" on functionality. This means that whenever a file is created, saved, moved, copied or deleted Spotlight is there to update its index and catalog so that it is ready for the next user query.
There are many more features, you should really check out Apple's web site for details.