The 10.6.4 Update is recommended for all users running Mac OS X Snow Leopard. It includes Safari 5 and general operating system fixes that enhance the stability, compatibility, and security of your Mac, including fixes that:

resolve an issue that causes the keyboard or trackpad to become unresponsive
resolve an issue that may prevent some Adobe Creative Suite 3 applications from opening
address issues copying, renaming, or deleting files on SMB file servers
improve reliability of VPN connections
resolve a playback issue in DVD Player when using Good Quality deinterlacing
resolve an issue editing photos with iPhoto or Aperture in full screen view
improve compatibility with some braille displays

System Requirements
Mac OS X 10.6.3