Dead Tracks
Those dratted exclamation points! (as you so unflatteringly refer to them) are what Apple calls dead tracks.
In brief, a dead track is one for which iTunes cannot find the corresponding file. This can happen if you rename a file or delete it outside of iTunes. Usually, you see this message for a fleeting moment when synching with an iPod. You recognize dead tracks by the exclamation points in the left margin, but iTunes gives you no way to track them down.
iTunes Toolkit can find and list all the dead tracks in your iTunes library. If you are using iTunes 8.1 or newer, you have the option of repairing dead tracks, in cases where the files have been moved or renamed. Alternatively, iTunes Toolkit can delete the tracks from your iTunes library.
