Although it hasn't exactly exploded into the mainstream music-listening population at large, the music-sharing application Simplify Media has a growing network of fans. When you install it, you must choose synchronization with with either Winamp or iTunes playlists, although you can change your preferred program after installation.
After setup and a restart of your music player, you'll see a "Simplify Media" selection in your left-hand navigation. Expand it, and you can browse all of the music available from you and your friends. A separately running Simplify Media application accessible via the Windows taskbar lets you add other friends with Simplify Media accounts and customize the program settings.
Claims of resource hogging and installation headaches are somewhat valid. Installing Simplify Media on Windows will likely require Apple Bonjour. It's included in the Simplify Media installation, but the slow download and subsequent install grated the nerves. Running Simplify Media, Winamp, and Simplify Media Peer, the process that streams media from your friends or remote computers, together uses more than a fair chunk of RAM.
Make no mistake with the minor quibbles: Simplify Media is an excellent and simple method of sharing music collections with friends or yourself in remote locations. We would like to see future versions become even more stable, as well as adding compatibility with other jukebox players.