To be fair, this is a pretty niche problem - tends to only be a problem when dealing with live music. So for example, if I have a concert recording, and make a playlist of those files for use in Spotify, Spotify will almost certainly replace at least one of those files with an album cut from the service. Now I'm left with a playlist of a live show that has had several tracks replaced with the _wrong_ version by Spotify.
The thing that initially drew me to Spotify was the fact that it made it pretty easy to integrate the music offered by the service with my personal library. I've always been disappointed that this feature was broken and left broken because the vast majority of people don't care about managing their own music libraries.
I'm a little salty about them closing off third-party development, but it's cool, they can do what they want with their stuff. I saw the writing on the wall a while ago when they were pushing Facebook integration like crazy -- as they become more and more anti-consumer, I'll simply avail myself of their services less and less until they offer me no value.