Removing songs with exclamation marks in your iTunes library.
This really works.
If you have iTunes on your PC, you may have tons of exclamation marks besides songs that are no longer in their original location, so iTunes can't find them.
You can't sort iTunes by exclamation marks, to easily remove them, but there is an easy way to find and delete them all at once.
Select all the songs in iTunes. Shift+End works for me.
Right-click any entry and select Get Info.
You can use any field that you don't normally use, but I used the BPM field and entered a value of "1." iTunes will enter this value in the properties of every song that it finds. If it can't find a song, it will leave the value empty. This process can take several minutes, if you have tons of songs.
When its finished, sort all the songs by BPM. Do it the same way you would sort songs by artist, album title, etc.
After the songs are sorted, all the ones with exclamation marks will be near the top. Just highlight them and delete them.
PS. This wasn't my own discovery. I googled around and found this suggestion.