The Fidelius Charm

Was just reading in HBP Snape saying to Bellatrix that he couldn't tell her where the headquarters for the Order of the Phoenix were because he wasn't the secret keeper, he couldn't speak the place name. Yet, surely there's more to it than not being able to speak the name of a place. I mean, if it comes down to knowing the address then surely Bella already knows that - the Blacks were relatives of her's. Just wondering if anyone has any insights on it. I've read Flitwick's explanation of it in book 3 and the use of it in book 5 of course, but I'm still puzzled. BTW, what's the likelihood that Rowling's not finished with the use of this charm?

Bella doesn't know that Sirius' house is the headquarters.
Apparently, no one has thought of the place in years.
She can't visit without an invitation because of all the old protections the family left.
And Sirius wasn't likely to invite her, even before she killed him.

Snape could probably drop a useful hint if he wanted to, as Kreacher did.
I suppose the Order will need to abandon the place now, not knowing what Snape will do.

The fact that Dumbledore's alive will need a Fidelius Charm before he starts letting people know. Maybe this time he will have the sense to be his own secret keeper.

New question: Why didn't Voldemort use a Fidelius Charm for his horcrux program? Or did he?

Could someone discover the secret of a Fidelius Charm on his own?
(Dumbledore figured out the horcruxes.)
And if he does, could he share the information?
(With Harry?)

"An immensely complex spell involving the magical concealment of a secret inside a single, living soul. 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" (PA10).

Single, living soul. Do they mean single as in one persons soul, or single as in, your soul can't be split.

Can you be your own secret keeper?

I think it has to be kept inside someone else, by the looks of it. It would be the ultimate in trust though and would also create a bond between to wizards/witches.

Nice work on it being inside a single living soul Seriously. I never noticed that before. It begs the query of course, what happens when that single living soul dies? Does it give up the secret or does it take it to the grave?

Why?

See the thread, "What Happens When Secret Keeper Dies," in the Div Class for Book VII.
...and the discussion goes on from there.