We have a quick update for Linux users.
We recently updated the signing key for Linux client upgrades. Linux users on recent version shouldn't notice anything--but users on older versions will need to manually add the new key.
At that link you can find a build of Spotify for Linux. We are running this ourselves and we will try to make sure it keeps pace with its Mac and Windows siblings. However, this version is unsupported. You can tell us what you think and ask other users for help at The Spotify Community.
Spotify for Linux is released as a Debian package. Our aim is that it should work with the latest Long Term Support release of Ubuntu, but we will try to make it work for other releases of Ubuntu and Debian as well.