Before I purchased the GN, I was really concerned about how the audio quality would turn out. I produce music and DJ on the weekends, so I am a little more aware of differences in audio quality than the average listener.
I tested the stock music app, and Power Amp--I have to say... I am impressed. In the past hour, I've listened to about 15 different genres of music through my monitoring headphones, and the results have been noticeably better than what my Droid X was able to produce.
Also, for the hell of it, I threw on some less professional headphones, and was still really enjoying the quality.
Feel free to post up any other music apps, or things that others could benefit from.