After merging 2 or 3 different iTunes libraries together, I gradually realized that my library was now full of duplicate files. Many songs existed in duplicate versions, with different file names, but same song, type and bit rate. Only one was showing up in my library, but the others were out there in the folder where I keep the tunes, taking up space. TuneRanger has a utility to remove disconnected files, so I gave this a whirl -- and it worked! Worth the price of admission for me.