"About MacBook Pro Retina SMC Update v1.1 (504KB)
(Link is now for SMC Update version 1.2 to fix a different problem than v1.1.)
This update resolves a rare issue where users may experience slow frame rates when playing graphics-intensive games on the 15-inch MacBook Pro with Retina Display. It also includes bug fixes for Power Nap, fan speed control and wake from sleep.

After this update has successfully completed, your SMC Version will be: v2.3f35

System Requirements: OS X 10.7.5 or later, OS X 10.8.2 or later"

The 10.8.3 update is recommended for all OS X Mountain Lion users and includes features and fixes that improve the stability, compatibility, and security of your Mac, including the following:

(list of fixes later expanded)
• Ability to redeem iTunes gift cards in Mac App Store using your Mac's built-in camera
• Boot Camp support for installing Windows 8
• Boot Camp support for Macs with a 3TB hard drive
• Fix for an issue that could cause a file URL to quit apps unexpectedly
• Fix for an issue that may cause Logic Pro to become unresponsive with certain plug-ins
• Fix for an issue that may cause audio to stutter on 2011 iMacs
• Fix for an issue that may cause the screen to display incorrectly after waking from sleep
• Fix for an issue in Messages that may cause messages to appear out of order after waking from sleep
• Fix for an issue that may cause the desktop picture to change after logging out or restarting
• Improves compatibility with IMAP servers in the Notes app
• Allows the Slideshow screen saver to display photos located in a subfolder
• Fix for an issue in Contacts that may cause cards to print out of order
• Fix for an issue in Contacts that may cause addresses to print in the wrong location
• Reliability improvements when using a Microsoft Exchange account in Mail
• A fix for an issue that could cause link aggregation to not complete after a restart
• A fix for an issue that could cause delays when logging into an Active Directory account on high latency networks
• Xsan reliability improvements
• Fix for an issue that could cause Active Directory accounts to be locked out after accessing the Security & Privacy pane in System Preferences
• Includes Safari 6.0.3

(See doc below for security fixes)

Here are OS X 10.8.3 articles on changes/security fixes and delta/Combo Update download pages.

Related Docs
• About the OS X Mountain Lion v10.8.3 Update (no longer online)
• About the security content of Safari 6.0.3
• About the security content of OS X v10.8.3 and Security Update 2013-001
  
  Download pages (no longer online)
• OS X Mountain Lion Update v10.8.3
• OS X Mountain Lion Update v10.8.3 (Combo)

OS X 10.8.3 release build is 12D78.

You can check Apple's OS X Mountain Lion Forum for feedback/any common problems reported. For mac model specific issues/fixes, check the forum for your model. Saw a post in the mac mini forum (in previous thread) noting improved display color/contrast after the OS X 10.8.3 update and the long MacBook Pro thread on WiFi issues had some posts it was not fixed in OS X 10.8.3. There's also reports of better PC nvidia card support/improved drivers.
(BTW: On a Late 2012 Mac Mini (2.3GHz Core i7/16GB ram/Intel 520 SSD) I saw a surprising increase in Cinebench OpenGL scores with OS X 10.8.3 - 26.51 vs 22.85 with OS X 10.8.2.)

FYI/Warning for Intel X25 SSD Users:
There's several reports from Intel X25 SSD users that it requires the latest firmware to be compatible with OS X 10.8.3. Otherwise it will not boot on a restart after the update. (2013 link to Intel's SSD firmware update tool download page no longer online.)
BTW: No problems updating to OS X 10.8.3 in a Late 2012 Mini with Intel 520 series SSD boot drive. (And an OpenGL CineBench score boost as noted above.)
 

"About Security Update 2013-001 (Snow Leopard)
Security Update 2013-001 is recommended for all users and improves the security of OS X.
For information on the security content of this update, please visit this website:https://support.apple.com/kb/HT1222
(here's the specific doc on security fixes in the update)

SHA1= dc52d0f7d2db6080c57c7b9252a4d85c5e178450

System Requirements: Mac OS X 10.6.8"

(The Download pages for Client and Server linked here in 2013 are no longer online.):

• Apple store has iMacs with Built-in VESA Mount Adapter (in 2011 $40 extra)
  
  
• 2012 Mac Mini user's Tip for Dell 2413 Display problem (apple mac mini forum)
  
  
• Jobs to be manga hero in Japanese comic series (pocket-lint)