The next "killer app" will be the one that allows a person to find new music that he or she would never have even thought of looking for, but will enjoy ... such an application would ignore GENRE and simply focus on THE INEFFABLE ESSENCE OF PERSONAL PREFERENCE.

Have a look at audioscrobbler. thereTheir service links the music you're listening to to other peoples tastes and recommends music to you, regardless of the (perceived) genre.

There are plugins for a lot of player-software, amarok has audioscrobbler build-in, others will follow I think - it's fun to get suggestions for new music that actually fits.