I had mine stolen not so long ago (if you've read the RNSE theft thread). I had it replaced with the cheaper, less desirable Concert CD/radio system, after weighing up...... Do I want it to go through the hassle again? Did I find the RNSE features any good in the first place? Could I live without the RNSE? etc. I bought my A3 second hand, before anyone replies asking why I chose the RNSE in the first place.
The only thing I kind of miss is the SD card storage feature. Besides, I found the RNSE satnav system tedious compared to Garmin/TomTom systems which I find easier/quicker/more intuitive. It's also mounted a bit too low to look at for my liking. Map updates are costly from Audi, but are lifetime free for Garmins/TomToms. I also disliked the RNSE's default volume when you start the car, which was a bit too loud. And couldn't find a menu option to turn it a notch lower.