Last.fm: is a music recommendation service that displays to other members what you are listening to and vice versa.
From their site:
A scrobble is a little note The Scrobbler sends to Last.fm to let us know what song you’re playing.
Scrobbling helps us tell you what songs you play most often, which songs you like the most, how much you’ve played an artist over a certain amount of time, which of your friends have similar tastes… all kinds of stuff. By focusing on the music you already play we can help you discover more music.
These resources are taken from Deltina Hay’s critically acclaimed book, The Social Media Survival Guide, already in its second edition. Social Media Power readers can get a discounted copy of the book from the publisher. Learn more about Deltina and her availability for speaking engagements at Deltina.com. You may also enjoy listening to her video tutorial series on YouTube.