I mostly listen to local media (iTunes library) when I'm using spotify. This library is very well organized, with all origins specifications registered in the metadata. Because of this I find it very infuriating that Spotify seemingly randomly picks other metadata from internet, and replaces the correct info with rubbish like "what compilation the track may have been included in" or that it is a "Remastered year NNNN" version. This again populates my Spotify DB to the extent that my versions sometimes are replaced in local cache with the (rubbish) source internet versions Spotify have identified. First of all you need to prioritize what metadata is used; which should always be local first! Then you need to continually and critically scrutinize what media databases you are using, and prioritize these according to how high validation hit-rate they have. I also sync an iPod Classic with Spotify, and the problem described above is most prominent on this, as it has no internet access on it's own, but still gets Spotify-cached versions that I do not want. As above, the sync mechanism should use local files first, instead of using the cache.