Fidelius (long, contains spoilers for PoA and OtP)

[JoAnna]

No: HPFGUIDX 95012

Wildean wrote:

<<<As we know, "The information is hidden inside the chosen person, or
Secret-Keeper, and is henceforth impossible to find—unless, of course,
the Secret-Keeper chooses to divulge it."  Dumbledore has used the
Fidelius charm to conceal 12 Grimmauld Place, particularly in its
aspect as the HQ-Quarters of the Order of the Phoenix. Presumably,
members of the Order of the Phoenix know where they're based, as part
of the secret that's being Kept. 

But if anyone outside the Order finds out, then the secret is divulged
and the place is no longer protected by the Fidelius charm. But there
are several non-members of the Order of the Phoenix who know all about
12 Grimauld Place, and the fact that it's the Order's HQ. Namely Harry
Potter, Ron, Fred, George and Ginny Weasley, Hermione Granger,
Kreacher, Mrs. Black's portrait.

I'd say pretty much that constitutes divulgence. In that case, what's
protecting 12 Grimmauld Place now?>>>

JoAnna:
Here are my personal theories about the Fidelus Charm:

1.  The person/place under the Charm cannot be Secret Keeper for
itself.  That is, I don't believe that either James or Lily (or Harry,
for that matter) could be Secret Keeper for themselves due to the
nature of the charm.  I don't have canon evidence to support this;
it's just a hunch of mine.

2.  I don't think anyone BUT the Secret Keeper can divulge the
wheareabouts of the location under the Charm.  IMO, the words "The
Headquarters of the Order of the Phoenix are at 12 Grimmauld Place"
could have been flashed on the scoreboard at the Quidditch World Cup,
but no one would have been able to find it unless Dumbledore himself
had done the flashing.  I believe this because of what Flitwick (?)
said in the Three Broomsticks:  "You-Know-Who could have had his face
pressed against the Potters sitting-room window and he still wouldn't
have been able to find them!"  So, even if you know the address of the
location under the Fidelus charm, it won't do any good unless the
Secret Keeper tells you where the location is.  So, even though Harry,
Hermione, et. al. know where headquarters is, they could put a post in
the Gryffindor common room and still no one could find the Order
Headquarters.

Just my opinion...

- JoAnna