For a file this big I don't see much it's going to do for me. Why does it seem big? I am also looking at the Combo updater.

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