If you still think it's all about a "killer app idea" and not timing, execution, marketing and a million other things, you're doing it wrong.

Look, I created this thing for myself and figured it would be useful for others, too. I don't intend to steal your "great next killer app idea", and I already have more ideas than time anyway. Ideas are essentially worthless, everyone has an infinite number of them :-)

Furthermore, the mockups on my site are not password protected, so they're essentially public (although there is no easy way to find them). In other words, yes, don't use the site for secret stuff.