Mac OS X 10.6 Snow Leopard first debuted at Apple's 2008 World Wide Developers Conference, the company's annual get-together. Instead of new end-user features, the update focuses on performance enhancements, under-the-hood tweaks, and feature refinements. Among the noteworthy changes that 10.6 brings is the transition to 64-bit applications, Grand Central Dispatch, OpenCL, and built in support for Microsoft Exchange Server 2007 in Mail, Address Book as well as iCal.
The adjustments reportedly speed things up a bit, too. Apple claims their operating system update is quicker in more aspect than one, from faster installation times and waking from sleep, to shutting down. Meanwhile it's lighter than ever, with an installation footprint around 6GB. The update is only available for Intel-based Macs and has entirely dropped the PowerPC architecture of old.
As you probably already know, Apple is selling OS X 10 Snow Leopard for $29 - a figure that puts Windows 7's upgrade costs to shame.