Online services that let the user create a playlist are dime-a-dozen on the web and most of them work the same way.
Think of an artist or a song and the service either suggests a ready-made playlist or lists songs that you can then add and make a custom playlist out of. If you like the song, pick it, or else move on to the next song on the list.
The problem with such services is that they’re all essentially asking the user to do the job. And that In the 21st century, is not acceptable !
The reason that the likes of Pandora, Spotify and last.fm are popular is because they work without any human intervention and still seem to play all the songs that the user would love.
What if there was a service that’d create a playlist for me without asking me to add songs to it ?