In response to the thread's owner, I would like to share some of my experiences as a NORMAL user who has spent a year with N9 ( kindly take note that I am a normal user, not a dev!).

Critical apps:
- N9 QTweak ( I use this to increase font size in message SMS, increase Volume, create filecaseroot which can use to browse system files, enlarge caller ID avatar,etc...)
- Billboard (make N9's standby screen much nice and useful, see picture below this post)
- Call Recorder (auto record all in-out call, perfect!)
- Easy Answer (answer the call just by move near to your ear)
- FileCase (browse file and photo and what more? browse your cloud service (like dropbox, skydrive, google drive) right in this app)
- Home screen settings (change operation provider' name and much more...)
- myExplorer ( transfer file to/from PC easily via wifi )
- FasterN9 (currently use 1.1.3 and witness how N9 faster!)
- Extensions for Status Menu (for the one who donot dare to use much Tweat like me, to get status menu more function and notifications, see picture below this post)
- Meecast ( worth to replace stock one )
- Vibrateme ( phone vibrates as soon as your outing call is answered )

Web browsering:
- Firefox ( for flash video streaming, must have FlashPlayer installed )
- Opera Mobile Labs ( other taste of web browsering )
- Default Web ( daily use )
- Feeds ( cool default app to catch up with daily news)
- TMO forum app ( app to daily follow topics relating to N9, IT and so on...)
- Nokia Tennis ( update info relating to tennis around to world )
- Livescore N9 ( update info relating to football arount to world )

Chat-Blog:
- Facebook default
- Twitter ( not yet used )
- Skype, QuickYM
- Extraplugins Accounts UI (plenty of acc for chatting...)

Media:
- Cutetube ( my cool client for youtube, can play in background )
- Zing Music client ( local music client for MP3, online streaming w/o lag while doing multitask )
- FM Radio(by Andrey Kozhanov) ( Listen to local radio w/o internet connection, able to record )
- IP Radio ( internet radio )
- Open Video Player (play video in background)

Photos:
- Panorama
- Instago (client of instagram)
- MOLOME (like instagram, but I prefer this)
- Flickrup (udpated with daily cool photos around the globe)

Games:
- AirAttack
- Bejeweled 2
- Galaxy on Fire 2
- iStunt2
- Angry Birds
- Goldpick
( and a lots I think )

Office: (sorry I put much in this group!)
- CalQtlator (calculator and can record history )
- Translate Mee!
- TranslateAll
- MeeNote (client for cloud Symplenote)
- KeepPage Plugin ( return to page stopped last reading, office doc)
- Converter
- CuteMeter
- Luxmeter
- Velocimeter
- Decibel

Other apps:
- BigKeyboard ( you will see how big a keyboard of a smartphone is! )
- Ringingrestorer (very good app, can set to time the phone restore to normal status from silent, ex: after meeting, ect...)
- Call Timer ( alert how long your ongoing call is )
- Drop Cache (like a ccleaner)
- Firewall+Pro (stop spam sms, reject phonecall)
- GPSMeeFo (boost up the catching of GPS signal, very good in case GPS signal is low)
- Compass
- Hydra widget platform ( play HTML5 widget )
- Liveclock (make the clock icon live)
- MyMoves ( set up action with 2-finger move, 3-finger move,etc...)
- Lockscreen
- Location2sms
- MeeWiMan ( check which wifi signal is best )
- MyTopSites ( set highest browse sites to top in stock webkit )
- Organizer Feed (push the calendar to-do to feed screen )
- Pockeego ( a kind of bookmark on what you browsed and put on cloud )
- Remove sim shortcut
- ScreenshotMee
- Simple Mirror
- Sleeper (set time to stop a music player for example)
- SwipeManager (extend swipe actions )
- The Flashlight
- Wifi pass recovery (remember wifi pass)

( the list would be longer daily!)

And last but not least, I like to share some of screen shots of my device in which I have put new "clothes" on it, hope you find some joys in this...
Cheers!!!