iTunes, Exclamation Mark!
Many of you probably know, that beaTunes has the capability to find those songs that iTunes marks with an exclamation mark to indicate that it was unable to find the corresponding file. It's called Missing File Inspection.
It was recently brought to my attention, that there is another way to find at least some of the missing tracks: Just sort by location in beaTunes. All songs that iTunes does not even know the old filename for will show up as unkown.
Eine deutsche Beschreibung der Inspektion befindet sich zudem auf der Seite iTunes Ausrufezeichen.