Really?Yes.
I'll happily spill the beans during an interview,
That's nice, but what's the incentive for people to come interview with you, just to find out what you're doing? Like others have said, you don't have to give away deep, deep details, but you need to at least give an abstract description of what you're doing.
I just don't want to post it out there just yet (we're barely getting started).
I think you're worrying about this WAY too much. It's not like there's a gaggle of idea-starved hackers sitting around watching your job postings, just waiting for a chance to jump on your brilliant idea, execute it better than you, and steal your market from you. Somebody - I'm thinking Steve Blank, but don't quote me on this - said something like "If your idea is any good, you'll have to beat people over the head to get them to go along with it." I'd take that to heart if it were me. <shrug />
But if you really want to stay stealth, why not stick to recruiting locally through trusted connections? What you're trying to do here seems almost like a fundamental contradiction. "Advertise widely, but keep everything a secret." I'm having a hard time seeing how that's going to work.