Available via software update (Macs) and this download page - summary says "This update is recommended for all Safari users and features improvements to stability, compatibility, JavaScript performance and security. Requirements: OS X 10.4.1, OS X 10.5.2, Windows XP, Windows Vista" Apple also has posted some Safari 3.1 related docs with more details on the changes - see
"About the Safari 3.1 Update" and "About the security content of Safari 3.1". If you find this update fixes or breaks anything (including safari addons) let me know.