fidelius

what do people think about the fidelius charm in harry potter? can the subject of the protected secret reveal the information, or is it only the secret-keeper who can tell? i mean -- the only fideliused secrets we know about are (in phoenix) the location of the order headquarters, and obviously the house isn't talking; and (in prisoner) the james-and-lily-hiding-in-godric's-hollow thing, which, it's doubtful that james or lily would have given themselves up to voldemort, had they happened to meet him somewhere else -- though, of course, by then it would have been a moot point, wouldn't it.

but the question remains. the hiding place is protected with fidelius, so only peter can tell the secret, even though at least dumbledore and sirius know it anyway; but could james and/or lily have told, say, frank longbottom where they were hiding, and because he's not the secret keeper, they don't have to worry about him telling anyone else?