What is it about certain songs that can touch a piece of us? That special something that lets you build a rapport with our listening ears? My view is that it is the music that connects with a part of who we are, where we've been, and what we've been through; much like the subject of the last song-lyrics I posted goes on about.
Most people that I know, there tastes in music in some way reflect their lives. For me and one friend in particular, I've noted songs that we enjoy tend to be of a more 'pleasurable-painful' nature. Music that can make you remember the old hurts and the old joys gone by, and in some odd way let you touch base with that emotion and feel better for still being able to feel anything that all: or perhaps its just the parts of our existence just plain suck lol.
The songs that I love the most, tend not to be "happy" in nature, but more of a long sad tune. If it's hit my playlist countless times or I take time to stop and listen to it over the radio, odds are it invokes a strong emotion somewhere.
Someday I think it would be cool to read a systematic survey that tries to map peoples experiences to their musical tastes, but such a thing would be rather tricky to get any meaningful result IMHO.