I had all of my radio's output stop working on me once (I have the Harman Kardon found in all the other 5th gen GT's). FM, AM, USB, XM, didn't matter what the source was. I was in traffic anyway and instead of coasting, I sped up to the car in front of me so I could stop and restart my car. Radio worked fine afterwards.
Having said that, there are other minor quirks, particularly with the USB playback, such as the radio getting stuck on the current track, even when the track should have ended.
I wonder if the 2013 system is in better shape.