What do we mean when we say it today?
Nowadays, we like to think we've matured a little bit. So we use this phrase to mean something that is unusable. Just like that old doornail we talked about. But then we also use it as a joke. Like we said, real mature.
Shakespeare wasn't the only one who liked this phrase. Charles Dickens used it in A Christmas Carol when talking about Old Marley. And Charlaine Harris thought it a good title for her New York Times bestseller.
So as you can see, this phrase is far from dead.