Project Playlist beta is a "Social Music Experiment" as the website describes it. It is a website that allows you to search for songs and add them to your own playlist and then share this playlist with other members of the site. It also allows you to get a html code so you can post it on Myspace, Facebook, or any of your own webpages.
Remeber that project playlist is a beta right now meaning they are allowing the public to basically test it out and are also trying to achieve a little bit of popularity before they decide to add more to the site. Right now it sounds like they are working on putting up a "Featured Artists" section along with the others that are already up like 'Music Buzz', the 'Blog', and 'News' about the site and updates.
To be able to use this website you first have to sign up , but it is totally free to join. It also has an area for you to post a picture of something or of yourself. You can then browse through the music and other people's playlists and create you own playlists with up to 75 songs on each. I don't know if you are limited on the number of playlists you can have, but it is fairly hard to fill up even one playlist so chances are you won't ever need very many.
Some downfalls with the site is that some of the sites that you can add songs to your playlist from have some copyright issues with them. Also some of the songs aren't labeled right or don't even work so you always have to make sure that they are correct. So with that said go ahead and check out the site yourself. Poject Playlist