In iTunes, a very useful feature is the File » Show Duplicates menu item. As expected by its name, you can use this feature to help weed out duplicates from your iTunes library. However, many people (myself included) have different versions of songs, remixes and such, which will show up as duplicates when using this feature.
The solution is to hold down the option key prior to selecting this menu item. When you do, Show Duplicates changes to Show Exact Duplicates. In this mode, iTunes shows only true duplicates, and not remixes or alternate versions.
Oh this is so nice. I can get rid of a few (bunch) tunes that are replicants in so many ways.