Accidentally pulled more than one copy of Yesterday into iTunes and find yourself lamenting the wasted megabytes of precious hard drive space? Put iTunes on Double Duty—you can have the program seek out and round up duplicate songs. Just click the Library icon or a playlist icon in the iTunes Source list, and then choose File→Show Duplicates.
After iTunes locates all the dupes, it shows them in its main window with a notice at the bottom that reads, "Displaying Duplicates." Here, you can look through and delete extra copies you don't need. But before you start whacking away, make sure these are true duplicates—and not two versions of the same tune by different people, two separate performances (like a live and a studio version), or a version of the same song from its original album and one from a soundtrack compilation.
Once you've cleaned up your library, at the bottom of the iTunes window, click Show All to clear out the list of duplicates and show your full collection in all its glory.