Hahaha, this is simply answered by all three replies so far. Quite simply put (sadly) they just listen. I haven't been a musician ALL my life, and only a composer in the last little while however I always tried to appreciate harmonies in conjuction with melodies and etc. (though my greatest difficulty remains to be putting them together correctly myself hahaha). However, as I look at my friends, many of whom are pianists, but unappreciative ones at that, music is simply a noise, either satisfying or irritating. It is simply played in the background of whatever they are doing to amplify emotion (basically only concentrating on the melody). This is sad though, because they don't appreciate the journey, the variation, and development...etc. Interesting question though.