“We have delivered more than a thousand new features to OS X in just seven years and Snow Leopard lays the foundation for thousands more,” said Bertrand Serlet, Apple’s senior vice president of Software Engineering. “In our continued effort to deliver the best user experience, we hit the pause button on new features to focus on perfecting the world’s most advanced operating system.”
According to MacRumors:
A new technology called "Grand Central" will make it easy for developers to create programs that take full advantage of the power of multi-core Macs. Also introduced is Open Computing Language (OpenCL), which extends the computing power of the GPU to any application written with OpenCL commands. Snow Leopard will also raise the software limit for RAM to 16 TB.
Also introduced is Quicktime X, which "optimizes support for modern audio and video formats resulting in extremely efficient media playback." Safari will see a 53% increase in performance and Microsoft Exchange will be supported out of the box.
Snow Leopard is expected to be available in about a years time.