Setting SMG up with the Spotify desktop application is simple, open SMG, select "Spotify Desktop", and press start once you've got some music playing. SMG will start picking up song info automatically. No need to configure anything else.
To make SMG work with the Spotify web player, you need to first install our smg web plugin. Afterwards, you can simply select "Spotify Web Player" in SMG, and press start.
There are currently no known major issues with Spotify. If you're experiencing problems, delete your SMG/config folder and restart SMG. If it doesn't fix your problem, contact support firstname.lastname@example.org or on our Twitter