If you think about it, "God damn it" really shouldn't be a mild expletive (unless you're an
atheist I guess). I have been told that in
Norway, "god damn you" is the worst thing you can say to someone. When you say that you want someone to be sent to unending pain and misery, that
is pretty serious. Of course, since
computers and other objects can't really be sent to
Hell, maybe it's not so weighty in the normal context.
The common use of "god damn it" in English goes back a long way...during the Hundred Years' War (1337-1453), the French called the English soldiers "godams" because they used that phrase so often.