The TT is certainly a quirky creation. There are things I have run into while owning the car that have really surprised or intrigued me or that I feel are just useful to know. Most of these can't really be classified well so I'll just list them here.
-If you have a Bose system, there is a central speaker under one of the air vents on top of the dash.
-There is also a sunlight sensor, used for controlling the AC, in the same location.
-You can use the A/C controls to access onboard diagnostics. Link.
-There is a phone jack next to one of the cupholders. If I recall this is, in fact, used for the stone-age car phone option.
-Sometimes after you pull the cluster or disconnect your battery, the ambient temperature readout will read incorrect, negative figures. This can be fixed with another battery reset. This also happens to MkIII VW's.
-There are little tabs that cover holes on the passenger's side of the center console; these are used for a grab rail which can be bought as an OEM accessory. Modshack also makes one.
-The button on the E-brake likes to pop off with incredible speed on occasion when used.
-The windows on the TT roll down ever so slightly when you lock/unlock the doors to prevent smashing them upon closing the door.
-You can roll up your windows using your key (common knowledge, but hey). When locking your car, put your key in the door and hold it in one direction until the windows roll up or down (different direction for up/down).
-Using VAG-COM, you can program your windows to roll up or down with the buttons on your key fob.
-The fuel cap, while it has many pretty looking bolts around it, is only held down by 2 or 3 bolts (forget the figure).
-You can turn off your center display by tapping the "reset" button on the wiper stalk.
-There is a random serial-type cable in the trunk. I'm not sure what it's used for.
-Reinstalling the lower dash is a PAIN.
That's all for now.