Windows/Mac: When Apple added a "social network for music" to iTunes, at first you could only "like" or "post" songs you'd purchased or found in the iTunes Store. Now Ping explorers can share music from their own libraries.
If you've activated Ping from your iTunes sidebar, and maybe found it lacking before, now you can find a new Ping button when hovering over tracks in your Library, whether or not you grabbed them from iTunes. You can Like a track, Post about it to your Ping profile, or visit that artist's Ping page to get more of your music tastes into Apple's own social experiment.
The deeper Ping integration is an update to iTunes (version 10.0.1.22), available free for Windows and Mac systems.
iTunes [Apple]