eman

Mine has to be the rear foglight.

kerrydel1

Ditto.

Had it on my previous car and don't think I ever used it in 6 years.

Kerry

Toecutter

The owner's manual...

CEB

...I regularly drive in areas where a deer will rearend you if you don't have a rear fog...

Zendriver

Would be nice if you could modify those to be super bright, to ward off people following too close.

charliemike

I wouldn't know how to use it if I tried. So I guess that's the most unused feature.

The second is the ski bag.

SFV A4

It is quite brite. I used mine soley to give the hint to tailgaters to back off. It actually worked once. If it's on and you look back at signs you've just passed, they are lit up. The other thing these are used for is an unwritten Audi family thing where you put yours on when you pass another A4 you like.

AZ-A4ber

voice command

Toecutter

We get lots of inclement weather here, so I use my F/R fogs a lot. I would also LOVE a ski bag, but you have to buy the BMW option for that.

They look like this (that's not my finger in the bottom-right frame -- it's an eclipse):

Blake P

I use my rear fogs all the time in the winter because we get very thick fog. My most unused feature would be voice command. I tried using it once and didn't know the exact commands to make it do what I wanted, so I haven't bothered since then. Luckily, all the buttons are laid out nicely where it makes changing things very simple.