I generally agree with Corey - if you can't talk about your idea openly, you're only hurting your chances.
That said, if you have tangible protectable intellectual property, you need to take some protective measures and simply asking people to sign an NDA is probably not the best choice. Yes, signing an NDA does protect the "disclosure status" of your invention - as long as you ask recipients of your IP to sign an NDA, you have not disclosed your invention to the public, thus ensuring that your IP is still patentable.
However, keep in mind the NDA does not protect you from theft of the IP...
You really should talk to an IP attorney about filing a provisional patent (or just file your utility patent application). Once you do that, your filing date is established and you can talk freely about your idea for a year, prior to filing your utility patent application.
If your IP is not patentable and your business concept only has a time-to-market-based advantage, I think Corey's advice is more pertinent. The winner will be who can execute faster and with a product / service that customers find more attractive. So asking everyone to sign an NDA only hurts your ability to reach potential partners and customers.