New webapp SonicSwap hosts your iTunes playlists on the web and streams the music in them free and legally without requiring you to perform tedious file uploads or use any of your computer's upload bandwidth. SonicSwap doesn't host your gigabytes of music files—you just give it your current iTunes playlists, and it pulls the tracks and videos named in them from YouTube, and recreates them in a drag-and-drop web-based version of iTunes. Sign up for a free SonicSwap account, upload your iTunes playlists either via the web site or using an iTunes plug-in, and you can listen to and share your library's playlists (including Smart Playlists) at SonicSwap, which includes video playback of the YouTube clip. Here's a full screenshot what it looks like.
Here's a direct link to this playlist at SonicSwap so you can try it out.
In my tests, the Java applet that you upload your
iTunes Library.xml file with failed, but the iTunes plug-in is an alternative method. Here's a video from the SonicSwap folks that explains how the app works.
Once you've uploaded your library, you can make it public, add friends, find other playlists, and even download others' playlists to your current library on your computer. TechCrunch reports that because of the YouTube API, occasionally you'll get a bum song (like a karoake version), but my cruise through other users' playlists yielded good results.