Today I tried to use the iTunes-cover screensaver (for the first time), but my screen (and the preview area in the system preferences) simply stays black, nothing else happens.
Has anybody experienced this too or has an idea what to do?
Try the following:
Re-creating my iTunes library worked for me.
The procedure consists in moving the iTunes Music Library.xml to a different location, removing the iTunes Library.itl file and then importing the xml file to re-build the library.
The details are explained in this article on the Apple support site: iTunes: How to re-create your iTunes library and playlists