Say you throw in a disc with a handful of images on it. If you open an image and then close the image... you can't eject the disc because "the disc is in use by an application"
Apparently Preview won't let you eject it until you quit preview.
I'm guessing it's just a bug, but it's an annoying bug for those out there that don't know why they can't eject their disc.
Would someone confirm this?