Today I came across a nice linux command here for listing open files on any device or mount point which is useful in following situation.
# umount /media/usbdisk/
umount: /media/usbdisk: device is busy
so it lists programs using files in that filesystem which you can kill and then unmount it.
Update: Shifted to Blogger in draft but editor is not that good, many things are still missing like
preview, spell-check, hindi script, etc. but has many new features like new page elements, exporting entire blog, etc.