From Twitter’s official blog:
Every day, millions of people use Twitter to follow and share what they care about. Twitter users now send over 95 million Tweets a day, many of which are about the music they’re listening to.
Starting today Ping, iTunes’ new social network for music, and Twitter are making it even easier for people to share music discoveries with their friends by putting Ping activity, song previews and links to purchase and download music from the iTunes Store right in their Tweets on Twitter.com.
How does it work?
On Ping you can easily link to your Twitter account to instantly find Ping users among the people you already follow on Twitter.
Once you’ve linked the accounts, whenever you Post, Like, Review, or tell your friends why you purchased a song or album on Ping, this activity will also be tweeted to your Twitter followers – complete with playable song previews and links to purchase and download music from iTunes.
When you click on a Tweet that’s sent via Ping or that contains an iTunes link, you’ll see the song or album in Twitter’s details pane, with the ability to listen to song previews from iTunes, making the experience even richer.
iTunes song previews are available on Twitter.com in the 23 countries where the iTunes Store offers music.