Occasionally when listening to music I remember it's not scrobbled to last.fm anymore, and for a moment I feel as if that's a bad thing. Then I remember wasn't useful. I also remember how memorable times involving music are memories in my mind, not lists of songs on a web site.
It might be cool if last.fm supported journal entries linked to a particular range time and playlist of tracks listened then. I'm not sure if that would be useful because I'm not sure if I could put those experiences into words in an appropriate way, and I'm not sure if they'd be useful later. However, I'd be interested in trying.