The following information was provided by Apple. [source]
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About the OS X Mountain Lion
The OS X Mountain Lion v10.8.2 update is recommended for all OS X Mountain Lion users and includes new features and fixes.
Updating your system
You should back up your system before installation; you can use Time Machine.
Do not interrupt the installation process once you have started to update your system.
You may experience unexpected results if you have third-party system software modiﬁcations installed, or if you’ve modiﬁed the operating system through other means.
Choose Apple () menu > Software Update… to check for the latest Apple software via the Mac App Store, including this update.
Other software updates available for your computer may appear, which you should install. Note that an update’s size may vary from computer to computer when installed using Software Update. Also, some updates must be installed prior to others.
You can also download the manual update installer. This is a useful option when you need to update multiple computers but only want to download the update once. These versions of the standalone installers are available from Apple Support Downloads.
This update is recommended for all OS X Mountain Lion users, and includes new features and fixes:
- Single sign on for Facebook
- Adds Facebook as an option when sharing links and photos
- See Facebook friends’ contact information and profile pictures in Contacts
- Facebook notifications now appear in Notification Center
- Share scores to Facebook, Twitter, Mail, or Messages
- Facebook friends are included in Game Center friend recommendations
- Added Facebook “Like” button for games
- Challenge friends to beat your score or achievement
Other new features
- Adds Power Nap support for MacBook Air (Late 2010)
- iMessages sent to your phone number now appear in Messages on your Mac*
- You can now add passes to Passbook (on your iPhone or iPod touch) from Safari and Mail on your Mac*
- FaceTime can now receive calls sent to your phone number*
- New shared Reminders lists
- New sort options allow you to sort notes by title, the date you edited them, and when you created them
- Dictation now supports additional languages: Mandarin, Cantonese, Spanish, Korean, Canadian English, Canadian French, and Italian
- Dictionary app now includes a French definition dictionary
- Sina Weibo profile photos can now be added to Contacts
* Requires iOS 6
The OS X Mountain Lion v10.8.2 update also includes general operating system fixes that improve the stability, compatibility and security of your Mac, including the following fixes:
- Adds an option to discard the changes in the original document when choosing Save As
- Unsent drafts are now opened automatically when launching Mail
- Receive Twitter notifications for mentions and replies from anyone
- URLs are shortened when sending tweets from Notification Center
- Notifications are disabled when AirPlay Mirroring is being used
- Adds SSL support for Google searches from the Smart Search Field in Safari
- Adds a new preference to have Safari launch with previously open webpages
- Resolves an issue that may cause the “Enable Autodiscover” checkbox to always remain checked
- Enables access to the Mac App Store when Parental Controls are enabled
- Support for @icloud.com email addresses
- Resolves a video issue with some VGA projectors when connected to certain Mac notebooks
- Addresses an issue that may prevent Active Directory accounts from being locked out
- Resolves an issue that may cause the policy banner to re-appear prior to logging in
- Improvements to SMB
- Addresses an issue with NIS users when auto-login is enabled
- Addresses an issue in which the Keychain may not be accessible
- Ability to pre-authenticate a FileVault protected system
- Addresses an issue that may cause Xsan to not automatically start after migrating from Mac OS X Snow Leopard
For information about the security content of this update, please visit this website.