I have the same problem as beetlefrosch. I followed all the steps but the "Library update in progress" never ends. It's been running for 12 hours now and I only have a few playlists and I would not consider my iTunes library (if it is caching those images too) to be very large either. Is there any other way of getting this step completed or speeding it up ?
I'm using the latest version from the first post on the first page of this thread.
My Users/Spotify directory is not empty.
It contains the spotify-app-miniplayer directory, the css and js subdirectories and icon.png, in