This is a rough draft for a post addressing playlist sharing communities.
last.fm (was audioscrobbler) - Grabb.it - Project Playlist - Mix Matcher - Sound Flavor - Up to 11 - fiql - Radish - iondb - Kohvi Radio - imeem - Twones - Hypster - Plurn - mystrands - Chillface
Webjay.org and PortablePlaylist.com both purchased by Yahoo, who is expected to unveil their new playlist site any day now. iTunes allows you to publish iMixes, custom playlists of songs that are available from the iTunes music store. Rhapsody Unlimited subscribers are already paying a monthly fee for "all you can eat" music. And that means they don't have to pay specifically to hear your playlist.
Other Music Sharing Venues
mp34u - The Hype Machine (aggregator)
Muzic - Musical Taste - Mog
Playr - Digital Archive Streamer - Grabb.it
Related Mozilla Extensions
PagePlaylist - M3U Ripper - UnPlug