Got an OS X disk image that flat-out refuses to eject? Open a Terminal window and enter the following (remember to escape any special characters in your disk image name):
hdiutil unmount /Volumes/DISK_IMAGE_NAME -force
I haven’t had to use this that often with any of the recent releases of OS X, but the other day I yanked a CF card from a FireWire reader a wee tad too early. Result? A CompactFlash card in my hand and a very grumpy disk image on my Desktop. Whoops.