Hot on the heels of OS X Lion, released today, Apple has issued a new version of Safari, which includes some new features specific to Lion, but also contains dozens of security fixes. Safari 5.1 is included with Lion, and available for Snow Leopard (Mac OS X 10.6), and Safari 5.0.6 is available for Leopard (Mac OS X 10.5).
Lion users will have the new version of Safari in their new operating system. Users of Leopard and Snow Leopard can get the updates via Software Update. Full information about these updates is available here (Safari 5.1) and here (Safari 5.0.6).