If your business model is so fragile that merely discussing it threatens is a threat then you haven't got a business model at all.

Great businesspeople talk about their business. They tell everyone: Friends, strangers, potential customers. All kinds of people can provide useful feedback and the more you discuss your business the better an idea you're likely to have of how to build a good product.

Besides -- the only people who ever ask me to sign an NDA are the people who haven't got anything worth guarding to begin with.