I have a question about the fidelius charm. We know that DD's the secret keeper for the Order and its whereabouts, and that Wormtail was the secret keeper for the Potters. So, both times, the kept secret was a place. Does it work for other things than places? For instance, could Snape have a secret keeper for the fact that he's a spy so that he could spoil Death Eater operation, give secret information to the order or even wear a button saying "I'm a spy and you suck!" without Voldemort realizing the truth? That would explain a lot.
And what happens if a secret keeper dies? Is the spell broken?