a quick tip: the disk "name-here" is in use and could not be ejected

Under Leopard I seem to get this error relatively often when I'm trying to eject my external disks. Even after quitting all my applications, the error doesn't go away. I never want to disconnect my drive without unmounting it (maybe it's an OCD thing). Here's my solution:

First, get the device name of the drive: Disk utility > Select volume > Click Info > Then note the disk identifier.

Open up terminal to check which applications are using this drive (substitute your drive name):

lsof /dev/disk2s10

Quit (or kill) all the processes that are using the resource. If nothing is returned (as is frequently the case with me), then force umount the drive (substitute your drive mount point):

sudo umount -f /Volumes/Backup

I'm adding this because the man page on umount doesn't document the force (-f) option.