Alot of users have touch screen computers, devices, etc. It would be great to have a Jukebox Mode like the touch screen jukeboxes seen at bars, etc. Where you can scoll through playlist albums/songs, and the ability search for songs that aren't already on a playlist. (maybe auto add to a seperate jukebox playlist?) That way when having a party or get together anyone can pick songs that they want to hear to add to queue and just play random playlist songs when no other songs have been queued up.
A chat box (kind of like what is used in Sound Drop) is practically essential in the collaborative playlists. The whole reason for sharing music is so you can enjoy and discuss it together. Let me know if this is possible! :)
Also the capabilities to comment on all people's playlists, songs, etc....but im sure thats in the works already...
A jukebox feature has already been suggested here:
http://community.spotify.com/t5/Spotify-Ideas/Juke
Add your kudos there please - the existing kudos here will be added soon! ;)