Ireth
Myth Weaver
I think the problem I have with concealment comes when a plot relies on Big Secrets to work. If revealing the secret(s) means the central conflict would fizzle out and the characters would get along with each other, I often come away thinking the characters are nitwits. It's similar to doing a twist ending. When it works, it's fine; otherwise it can feel contrived. It should feel natural and not like the author is pulling the strings, even though she is.
That makes me think long and hard about my Fae duology; the whole plot of the second book hinges on the identity of one central character being concealed until the climax. Granted, she has very good reason to hide her identity, as the characters she interacts with are essentially unpaid bounty hunters, ordered against their own wills to bring her before the Kings of Faerie on pain of imprisonment or torture if they should fail or try to disobey the command. All of them consider her (her real self, not the persona she takes on to hide) to be their friend, but she doesn't trust them not to hand her over the moment she reveals herself, and they have a hard time even trying to get the point across that no, they do not actually intend to hand over their target to the Kings -- mainly because said Kings are tracking their every move, and whatever they say may be overheard.