The latest OS release fixes some niggling issues and hardens security. It also helps prepare Mac users for the upcoming release of Mac OS X Lion. Mac OS X 10.7, also known as Lion, is due out next month and will be available exclusively from the Mac App Store for $29.
Full release notes are available from Apple. Users who need the full combo updater (roughly 1GB in size) can download directly from Apple.
Source : Mashable.com