Headline pretty much says it all, and it's a big one. Tipping the scales at 377MB (or 190MB for some; see image after the break), the OS X 10.5.6 update is now available via Software Update. We're sucking it down and will report back with any changes. We strongly encourage you to do the same (if you dare).

Update: Apple has posted the official changelog. Here are the highlights:
  • Improves the reliability of AirPort connections, including improvements when roaming in large wireless networks with an Intel-based Mac.
  • Improves reliability of Address Book syncing with iPhone and other devices and applications.
  • Includes general improvements to gaming performance.
  • Includes fixes for possible graphics distortion issues with certain ATI graphics cards.
  • 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.
  • Improves Apple File Service performance, especially when using a home directory hosted on an AFP server.
  • Improves reliability and performance for AT&T 3G cards.
  • Improves printing for USB-based Brother and Canon printers.
  • Fixes issues that could cause Time Machine to state the backup volume could not be found.
  • Improves Time Machine reliability with Time Capsule.
  • Adds a Trackpad System Preference pane for portable Macs.
  • Personal Engadget favorite: Improves the performance and reliability of Chess.
  • Nary a mention of Blu-ray. It's still hurting, we guess.

[Thanks, Fraser]