Since I know that most of Katy Perry's music except for some of the remixes for some of her singles are not avalible on Spotify, my suggestion is to have some sort of request form with tracking on what we would like to be able to complete the set without having to buy the content on iTunes instead.
Don't get me wrong, I do like Spotify's services and how they are working to try and get more of the music onto their services, but sometimes I just find it frustrating that even as a premium membership holder, I would still have to import that content onto Spotify in order to use it within their services.
I don't blame Spotify since they cannot reach an agreeement with the record labels. I just hope there can be some sort of request form for a certain album/artist/soundtrack instead of having to tweet/email and miss details in order to see if that request can be done. What I also hope for if they do consider a suggestion form is also provide tracking or have a list of most reuqested albums/soundtracks/artists and what the pending status is for completing that request.
Just my feedback on how simply requesting music that isn't currently on Spotify and seeing if there could be an easier way to see if a request can be done.
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This is already implemented, take a look at the music FAQ.