I use collaborate playlists to introduce friends to new songs I found that I think they'd like. It would be nice to have a feature where in collaborate playlists, followers can like/rate the songs. So, for example, if I add a song, then another follower of the playlist can hit 'Like' - not to add it to their liked songs, but so I know they liked it. This would make it easier for me to know if my friends like the songs I'm adding or if I'm adding songs they don't enjoy. It'll make it easier to find out what songs to add that I think they'd like.