I didn't make this thread. Whoever made this thread last year did it and it was great. if he didn't want the responsibility he shouldn't have jumped to make this thread thats all.
the OP could start with this and then add anything else thats missing.
Usage
Time since Last Full Charge for iPod and iPad.
Siri (iPhone 4S and iPad 3rd Generation Only)
New Languages: Canadian English, Spanish (Spain/Mexico), Italian, Switzerland (Italian), Korean, Mandarin (Mainland China/Taiwan), Cantonese (Hong Kong/Mainland China)
Siri for iPad (3rd generation)
Siri can now provide information on Sports leagues such as NFL, MLB, NBA, NCAA Basketball and Football, WNBA, English Premier League, MLS, and more. Ask for player stats, team rosters, game schedules and team standings.
Siri can provide information on movies like find movie reviews, ask about actors and actresses, play a movie trailer, get showtimes for movies and find a theater.
Yelp! built-in reviews and launch to open up more information and create reservations with OpenTable.
Restaurants are listed by reviews and nearest with more information
Apps can be launched by saying "run <app name>" or "open <app name>"
Facebook updates and Twitter tweets can be posted from Siri.
Have Siri read your Notification Center updates.
"Eyes Free", allowing for cars to integrate with Siri with a mic button on steering wheel and for launching Siri functions. Screen is disabled during Eyes Free mode
Local Search now works around the world.
Facebook Integration
Facebook integrated into core applications on iOS 6; similar to Twitter integration in iOS 5
Integrated into Notification Center
Integrated in Siri and APIs for third-party apps
Address book can sync contact information from friends on Facebook
Facebook Events and birthdays in Calendar
Like button on apps and content from the App Store and iTunes Store.
Passbook
New app that manages a user's boarding passes, movie tickets, retail coupons, loyalty cards, etc. in one app. Similar to Newsstand.
Store coupons and gift cards in a wallet-like app (Starbucks, Target, Apple Store)
Airplane boarding passes for flights; updates boarding pass information in real time if changes are made
Passes are location and time-based. They appear on the lock screen when necessary
Notification Center
Update Facebook status or tweet from new widget
Message previews can now be toggled off and on for alerts
Photos
Shared Photo Streams. Photos can be shared with other contacts. Photos shared can be commented on and liked. Notifications are enabled for when a contact shares a photo with the user
Music
New streamlined UI with white and black themes with silver slider controls that change their shine angle based on accelorotmeter data. (iPhone/iPod touch only)
Late Night Mode equalizer.
Settings
"Bluetooth" moved to top of Settings list
Added "Do Not Disturb" mode, allowing users to avoid calls and notifications unless calling parties are on the user's Favorites group
Added in Notifications: Government warnings and AMBER alerts can be toggled on and off
Privacy Controls
A slightly changed Icon.
Phone
Adds phone icon on lock screen for additional ignoring options, similar to the camera sliding icon on the lock screen in iOS 5.1
When ignoring a call, the user can message the caller or set a Reminder to call them back later
Phone call doesn't take up the entire lock screen when a call is incoming
New white themed UI for dial pad.
Maps
Turn-by-turn Navigation with Siri Voice powered by Tom Tom (iPhone 4S and iPad 2 or later, voice directions for iPhone 4S and 3rd generation iPad only)
Maps are now Apple-sourced instead of using Google sources.
3D overview (iPhone 4S and iPad 2 or later)
Satellite view
Flyover view for maps gives 3D satellite view (iPhone 4S and iPad 2 or later)
New Map icon
Lock Screen integration for turn-by-turn navigation (iPhone 4S and iPad 2 or later, voice directions for iPhone 4S and 3rd generation iPad only)
Yelp! integration available for businesses near the user gives provides reviews and information on the business. Allows the user to launch Yelp! from Maps
Info cards of businesses
Traffic crowd sourcing with anonymous data sent from all iPhones also adds events of traffic slow down
FaceTime
Make FaceTime calls over 3G or LTE cellular connection (iPhone 4S & 3rd generation iPad only)
Mail
VIP inbox stars important emails from user defined VIP group members
Flag emails
Attach photos and videos quickly with a tap
Open password-protected Microsoft Office documents
Added Pull-to-Refresh to update Mail accounts
Per Account Signatures
Contacts
Search All Fields
Custom Vibrations for Ringtones & Text Message Notifications
Reminders
Manual Reader
Manual location based reminders
Location based reminders
Safari
Fullscreen landscape activated with a tap
iCloud tab syncing across devices
Offline reading list caches the user's reading list for later use, even when not connected to the Internet
Smart App Banners: Banners on mobile webpages prompt users to download the website's native App Store counterpart in the App Store
Faster JavaScript engine
Apps in search results
Support for photo upload via Camera Roll
Support up to 24 open tabs on iPad.
App Store
New UI
Darker theme
Applications can be purchased from within apps.
Installing an app no longer returns the user to the home screen the app will download and install while continuing to browse the store
Updating an app no longer requires the iTunes password to be entered
iTunes
New UI
Darker theme
Content can be purchased from within apps.
Accessibility
Guided Access:
Allows user to lock exiting of the app in Single App Mode.
Allows users to disable certain controls within a specific app.
iCloud
Personal Dictionary synchronization.
Clock
Alarm can be set to any song in Music app
Clock app added to iPad.
A slightly changed Icon.
Weather
A cleaner and slick new UI.
Game Center
Game Center challenges
Facebook friends integration
Camera
HDR improvements
Darker theme
Security
Kernel ASLR added
Other
Lost Mode: If iPhone is lost, Lost Mode triggers an attention grabbing sound, and prompts the person that finds the iPhone to call a specific number set by the owner remotely
Additional features for China
VoiceOver improvements
Custom Vibrations for Alerts
Global Network proxy for HTTP
IPv6 support for Wi-Fi and LTE
Word highlights for speech support
Auto Correction for every keyboard
Bluetooth Map support
Improved keyboard layouts
New Thai Keyboard (Full Keyboard)
French, German, and Spanish Dictionaries
Made for iPhone hearing aids
A blue "New" ribbon over freshly installed apps
Status bar reflects the colour of the top-most banner in 3rd Party apps
Spotlight lists name of folder an app is located in
Support for US Government Wireless Emergency Alerts