For me, old mirrors hold stories from the past and can bring a unique feel to any room. I like mirrors with personality - evidence that they've been a daily part of someone's life. I'm not concerned if some of the silver is worn off the back or if there are scratches and nicks. To me, it's all part of their charm.
I like to arrange a few on a shelf, a table top, or a wall to create a bright corner in the room. Any place is a good place for an old mirror or two - or three.