Ever since the creation of Google+, Google has been working to integrate all their products into one cohesive ecosystem by providing various hooks into their social networking offering. One of the most interesting came with the introduction of Google Music.
Google Music users who purchased songs or albums through the online service could share their purchases to their friends and followers on Google+ where these friends could listen to the purchase in it's entirety. This served as an excellent tool to hook people into using both Google+ and Music and served to propagate music discovery which would lead to further music sales.
Google has slightly tweaked Google Music's web interface to include a 'Shared with me' auto playlist which is populated with all the songs people in your Google+ circles have shared. All the songs are now gathered into one easily accessible playlist instead of forcing users to backtrack through Google+ pages to finds shared music.