Every now and then I scroll through my "Recently Added" tab on iTunes, going all the way from when I first started ripping mp3s in the 7th grade, to today. I'll see that time I went on a 12-month Memphis rap binge in college. Or when I came back from 5 months in London and was suddenly "into" dance music. One of my favorites is revisiting the summer where I started to really dig through Madlib samples.
Huge blocks of my life are mentally categorized by the music that I was listening to at the time. For me, Lettermans is just a way to make that timeline public and to share conversations with my favorite artists. For you, it's hopefully a reliable place to learn something new.