Q: I’ve been using my iPod as a hard drive to take files to and from work and college. I’m done with the files and went to remove them from the iPod. The OS X Finder shows that they are no longer there, but the free space didn’t change. I tested to see if it works properly in iTunes when I delete a song, and it works fine.
A: The most likely issue here is simply that you have not yet emptied the Trash. When storing files on your iPod, it literally works just like any other portable hard drive, and will therefore have its own trash folder. As with your normal System drive in OS X, files continue to consume disk space until they are actually emptied from the trash.
Ensure your iPod is connected to your computer and showing in your Finder window or on your Desktop, and choose Empty Trash from the Finder menu. The files on your iPod’s file system trash should be removed and the disk space should again be available for use.