the sound is actually fine on a set of decent ear buds. But I mostly listen to audiobooks rather than music or the odd podcast of some sort, I like Spider Robinson's podcasts as a rule and am always in the mood for a WWDTM or Car Talk episode or two.
Still given a choice I prefer a small MP3 player to using the Kindle because if I just want to listen to something it's hard to walk and use the Kindle to play something though I have made it work as a why-not-try-it sort of thing.