Announced at WWDC
A Quantum Leap.
Since 2001, Mac OS X has delivered more than a thousand innovative new features. With Snow Leopard, the next major version of the world’s most advanced operating system, Mac OS X changes more than its spots, it changes focus. Taking a break from adding new features, Snow Leopard — scheduled to ship in about a year — builds on Leopard’s enormous innovations by delivering a new generation of core software technologies that will streamline Mac OS X, enhance its performance, and set new standards for quality. Snow Leopard dramatically reduces the footprint of Mac OS X, making it even more efficient for users, and giving them back valuable hard drive space for their music and photos.
64-bit
To accommodate the enormous amounts of memory being added to advanced hardware, Snow Leopard extends the 64-bit technology in Mac OS X to support breakthrough amounts of RAM — up to a theoretical 16TB, or 500 times more than what is possible today. More RAM makes applications run faster, because more of their data can be kept in the very fast physical RAM instead of on the much slower hard disk.
Taken from http://www.apple.com/macosx/snowleopard/
Sounds like an exciting upate 
