As we announced it earlier, Mac OS X 10.5.7 was almost ready to be released, and Apple just did it:
The 10.5.7 Update is recommended for all users running Mac OS X Leopard and includes general operating system fixes that enhance the stability, compatibility and security of your Mac.
Apple also released Safari 3.2.3 for Mac OS X (distinct versions for Leopard and tiger) and Windows (This update is recommended for all Safari users and includes the latest security updates.) as well as the second security update of the year for both Leopard and Tiger (2009-002: Security Update 2009-002 is recommended for all users and improves the security of Mac OS X. Previous security updates have been incorporated into this security update.).
As usual with such OS update, you better clone/backup your system and data before installing Mac
