Very interesting stuff here guys. For me, the process is this:
1, You hear the song somewhere and it catches your attention. You find yourself needing to hear it again.
2. You subsequently get to hear it again, and it works its way into your brain, ticking all the boxes on your own personal 'What it is I like about a good song' list (which, for everyone is, of course, completely unique).
3. With repeated listens you fall totally in love with it, and every time you hear it, you have the sweetest little eargasms.
4. You get a recording of it and include it in your own personal and ever-growing musical harem (ipod, cd collection etc.) with all the other songs you love, and for as long as you live, it should remain high on your list of little musical masterpieces.
5. In time you will - of course - move on to the next one (because there are so many out there and it is impossible to remain completely loyal to only one), but you will always have a special place for it in your musical memory. There may be exceptional circumstances of course, where something really bad happens to put you off listening to a song ever again - an emotional trauma in your life, maybe; or even when the artist f*cks it up for you (like with the whole Gary Glitter paedophile thing - all those poor, betrayed little people who were seventies teenagers... it's not a wonder punk happened!).
There are so many reasons why you could judge a song to be 'good' - melody, harmony, counterpoint, lyrics, arrangement, atmosphere, purpose, relevance, etc... the point is that for you, it comes along at the right time and, for whatever reason, it really appeals to you and blows your socks off. The songs you love are part of the soundtrack of your life and their importance should never be underestimated. Don't you agree?