This update is recommended for all OS X Mountain Lion users, and includes new features and fixes:
Facebook
- 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
Game 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
