To create Snow Leopard, Apple engineers refined 90 percent of the more than 1,000 projects that make up Mac OS X. Users will notice refinements including a more responsive Finder™; Mail that loads messages up to twice as fast;* Time Machine® with an up to 80 percent faster initial backup;* a Dock with Exposé® integration; QuickTime® X with a redesigned player that allows users to easily view, record, trim and share video; and a 64-bit version of Safari® 4 that is up to 50 percent** faster and resistant to crashes caused by plug-ins. Snow Leopard is half the size of the previous version and frees up to 7GB of drive space once installed.
For the first time, system applications including Finder, Mail, iCal®, iChat® and Safari are 64-bit and Snow Leopard’s support for 64-bit processors makes use of large amounts of RAM, increases performance and improves security while remaining compatible with 32-bit applications. Grand Central Dispatch (GCD) provides a revolutionary new way for software developers to write applications that take advantage of multicore processors. OpenCL, a C-based open standard, allows developers to tap the incredible power of the graphics processing unit for tasks that go beyond graphics.
Snow Leopard will be available as a upgrade to Leopard (10.5) for $29 or $49 for a five-seat Family Pack. A Mac Box Set including Mac OS X Snow Leopard, iLife '09 and iWork '09 will be available for $169 for a single user license and $229 for a Family Pack. If you purchased a qualifying Mac with Leopard installed after June 8, 2009 you can get a copy of Snow Leopard for a shipping and handling fee of $9.95 plus tax via Apple’s Mac OS X Snow Leopard Up-to-Date Program.
Full details are on Apple's product page: http://www.apple.com/macosx/.