I have a great idea, but I can't tell you - Primer in entrepreneurship

Nice article. I have met couple of people one with Marketing and Sales back ground and another with Finance background. Both had ideas but no developers to develop their product and were looking for a team of developers. They both insisted me to sign a NDA, before they could talk about their idea, I did.

I thought that was little weird for me because I thought both them would have at least 6 months ahead of anyone who tries to copy their idea, but they weren't thinking that way.

Is it ok to sign a NDA? Are there somethings to watch out for? With respect to these candidates, is asking for NDA right way to share an idea and collaborate with others?