Find unplayed songs in iTunes
A device like the 160GB iPod Classic can hold so much music, you could listen continuously for around 75 days and never hear the same song twice*. Of course, nobody does that--and let's not even go into how you scored 160GB of music without spending tens of thousands of dollars.
Most of us gravitate toward our same favorite albums and artists on a day-to-day basis, or put our iPods on shuffle. But for those completists out there, it can be frustrating to know there are songs hiding in your collection that you've probably never heard.
Who knows? Maybe your new favorite song has been hiding in the dark recesses of your hard drive all this time.
*Assumes songs are encoded at 192kbps AAC, with an average length of 4 minutes.