I've considered this a bit. Right now you can share those play links by posting a link to the song or album or playlist, but what you're listening to i like the idea of it being ephemeral, like you go to someone's house and they're listening to a song you like. It's not written down in a history log anywhere it's just there until it isn't anymore. It's what you're hearing when you walk in, not what's saved in a photo in a scrapbook.