I saw this idea in a house we went to view, in fact in the house which we are now buying! At the time I thought it was so clever I was determined to steal it and use it in wherever we actually did buy. Who needs a pin board when you can magnet paint a whole wall and then blackboard paint over it.
This pic isn't actually of our new place to be, but is a great example. I'll upload some pic of our version when we eventually get the keys.