I have plugins in Calibre that strips the DRM from books as I load them into Calibre. That way I know all the books have been "liberated"
I also back up my Calibre Library using the service Dropbox, that way I have a backup of all my books off site. I do this as I have had hard drives die on me in the past.
to get an account on Dropbox use this link
https://www.dropbox.com/referrals/NT...M5?src=global0
we both get an extra 250mb if you do :-)
I leave all the DRM books on the service website (mostly B&N) , as I can download them any time I wish