"About OS X Mountain Lion 10.8.5 Supplemental Update (18.74 MB)
The OS X v10.8.5 Supplemental Update is recommended for all users running OS X Mountain Lion v10.8.5. This update:

Resolves an issue that may prevent certain applications from using the FaceTime HD camera on MacBook Air (mid-2013) systems

Fixes an issue that may cause external drives to be ejected after the computer goes to sleep

Addresses an issue that may prevent HDMI audio from working after waking from sleep

Fixes an issue that may prevent certain USB Bluetooth adapters from working

SHA1: 18636c06f0db5b326752628fb7a2dfa3ce077ae1

System Requirements: OS X Mountain Lion v10.8.5"
(The OS X build after installing this update is 12F45)

Today's Apple docs list has one on a security fix in this update. (Apple also reposted OS X 10.8.5 updaters (delta/combo) that I assume include the Supplemental Update - see links below.)
You can check Apple's OS X Mountain Lion forum and the Desktop forums or notebook forums of your specific mac model for early feedback. As always, have a current backup. (I also like to have a bootable clone.)
Early feedback was positive from those that had problems with drives 'ejecting' in sleep (warning message on wake), drives going to sleep despite energy saver settings and no audio after waking from sleep. An early thread says installing the Supplemental Update results in the Mach_Kernel file being visible. Includes a post with terminal command to hide it. (FYI: On Oct 23rd, Apple posted a doc titled OS X: mach_kernel visible in the Finder with the same terminal commmand hiding tip.)

BTW: If you previously replaced the CoreMedia AppleCamera.plugin in OS X 10.8.5, the Supplemental update won't fix the Facetime camera/32bit apps problem but reinstalling the (Oct. 3rd) OS X v10.8.5 Combo Updater reportedly works.

(FYI: A reader said installing the Oct. 3rd 10.8.5 Combo Updater results in the same OS X build (12F45) as installing the Supplemental Update over a previous OS X 10.8.5 (12F37) install. And unlike the Suppl. Update install, the Mach_Kernel file stays hidden.)

Also a note from a reader says the Suppl update/build breaks the Nvidia driver update for 10.8.5 (12F37). (Update: On Oct. 9th Nvidia posted New Nvidia Quadro/GeForce Drivers for OS X 10.8.5 (12F45) + a CUDA Update)
  

• iTunes 11.1.1 (bugfixes)
• OS X Mountain Lion Update v10.8.5 (post date Oct. 3rd)
• OS X Mountain Lion Update v10.8.5 (Combo) (post date Oct. 3rd)
• 21.5" iMac review: Modest gains for entry-level Haswell iMac
• WD My Book and My Book for Mac Review
• Security firm says iPhone bug can thwart device wiper
• The iPhone 5S Motion Sensors are Screwed Up (not calibrated?)
• Other World Computing Hits 25 Year Milestone (sponsor blog)
• SEGA Superstars Tennis for Mac due Oct. 17th
• Yojimbo for iPad 1.1 Release Notes
• Yojimbo 4.0.1 Release Notes

• About the OS X Mountain Lion v10.8.5 Update (added Supplemental Update info)
• About the security content of the OS X Mountain Lion v10.8.5 Supplemental Update
  
  
• How to identify iMac models
• Apple Thunderbolt cables and adapters
• Mac computers: Liquid damage not covered by warranty
• Apple computers: Troubleshooting issues with video on internal or external displays
• MacBook Air (Original, Late 2008, and Mid 2009) Hinge Quality Program has ended
  
  
• AirPrint Basics (with list of compatible printers)
• Aperture 3: Tips on tethered shooting
• iCloud: Troubleshooting iCloud Reminders and Tasks
  
  
• iAd Producer 4.1: Release notes
• iAd Producer 4.1: iOS Simulator doesn't switch to iOS 6 if first opened in iOS 7 64-bit
• iAd Producer 4.1: iTunes Radio banner ads might not load from the iAd Server
• iAd Producer 4.1: iAd Producer quits unexpectedly on first sign-in to iAd Server
• iAd Producer 4.1: After tapping an iTunes Radio banner in the iOS Simulator, the ad's media does not play
  
  
• iOS: How to back up and restore your content
• iOS: Understanding Restrictions (parental controls)
  
  
• iTunes Store: Closed captioning
• iPod not recognized in My Computer and in iTunes for Windows

• iTunes 11.1.1 for Windows (64-bit) (download page)
• Adobe's Important Customer Security Announcement (regarding breach)

Wednesday Oct. 2nd, 2013 News Archive
• Apple hires cable TV exec for 'something big'
• Win Prizes with #25YearsofOWC Trivia Quiz (sponsor blog)
• Report: Apple to Fix iMessage Problems via iOS Update
• Sharper display Apple iPad Mini faces delay: sources
• Frax app brings fractal-exploration to iOS
• Best crime-fighting features of iOS 7
• Cocktail 6.8.1 (Mountain Lion Edition)
• New/Updated Apple Support/How-To/Troubleshooting Articles:
  - EFI and SMC firmware updates for Intel-based Macs (added new SMC updates)
  - Target Display Mode: Frequently Asked Questions (FAQ)
  - Apple TV (2nd and 3rd gen): About Apple TV and HDCP
  - iTunes: Syncing photos
  - iTunes: About iOS backups
  - iTunes: How to share music and video
  - iTunes: Setting up Home Sharing on your computer
  - iTunes Match on iPhone, iPad, or iPod touch
  - Managing your iCloud storage
  - Troubleshooting iCloud Calendar
  - Troubleshooting iCloud Contacts
  - iOS: Troubleshooting FaceTime and iMessage activation
  - iOS: Forgotten passcode or device disabled after entering wrong passcode
  - iPhone 5s: Using Touch ID
  - iPhone: Hardware troubleshooting
  - iPhone and iPad (Cellular Models): Understanding cellular data settings and usage
  - Obtaining iPhone Service in the European Economic Area (EEA) and Switzerland
  - Can't burn a CD in iTunes for Windows
  - iTunes 10.5 or later for Windows: Older media files may require QuickTime

For links to older news pages, see the Archives.