Adding support for virtual musiclibraries in Spotify

This is a great app, what I truly miss in it though, is the ability to create your own music collection. What I would love to see is sort of a private musiclibrary to which you add songs/albums you find in the big library. I would also love to see a way of creating playlists of this collection. The problem that this would solve for spotify is that it is really hard to have a "music collection" in spotify, sure - you can have multiple playlists, but that just doesn't beat the musiccollection we all have at home. If we could recreate i on spotify using spotify tracks this application would be the best online music service I have seen. Ever.