Elon Musk has recently released a technical, detailed, proposal-of-thought for something called the Hyperloop, and asked for feedback. As far as I can tell, much of the feedback that has cropped up publicly reinforces the technical feasibility of the Hyperloop but questions the economics behind it.
It is of course very different for someone like Musk — who can command major media attention over one of his ideas — than for most people, who would struggle to receive the kind of dedicated, detailed review of a fifty-seven page technical document that the Hyperloop is getting.
One thing I love though is that Musk is not afraid of idea theft. To be fair, the basic concepts behind the Hyperloop are not new; there is no grand secret mental breakthrough he is trying to protect. But what a poster case for not over-protecting your idea.
Many folks who set out to put a dent in the universe do so at first by hiding their ideas and intentions. But ideas are antifragile: they become more robust with discussion, disagreement, debate. In most cases, it is far better to share your ideas early, learn from the feedback you get, and adapt them.