The Mac OS X 10.5.6 Update is recommended for Mac OS X 10.5 Leopard versions 10.5, 10.5.1, 10.5.2, 10.5.3, 10.5.4, and 10.5.5. It includes general operating system fixes that enhance the stability, compatibility and security of your Mac.On a MacBook Pro c2d, it weighs 190MB, while it goes up to 377MB on an Unibody Macbook Pro...
The list of changes is HUGE and, for once, extremely detailed, and you can read it here.
And, by the way, the best feature probably? REAL PUSH UPDATES to MobileMe:
MobileMe: Contacts, calendars, and bookmarks on a Mac automatically sync within a minute of the change being made on the computer, another device, or the web at me.com.
