On Flickr, you can create a guest pass for private viewing of a single photo album (set). This makes lowers the barrier to share things with family/friends. It'd be great if we could do the same with music, ie. share a single playlist.
Use cases: perhaps you want to share some songs you recorded yourself with a potential producer, but don't want them to see those embarrassing Culture Club albums in your collection (sorry, Culture Club fans); or perhaps you want to share some _other_ music with your friends, and not have them laugh at the very private song you recorded yourself.
Then it'd be great if you could just make a playlist, click "create a guest pass for this playlist", and get a weird URL -- using this url gives access to this playlist, but nothing else.