Two words important to technical types: Working code.
For "pure" tech ideas -- where the product primarily consists of software with unique functionality -- these two things are equivalent, and staying in "stealth mode" and protecting yourself with NDA's until you're ready for release is important, because it's easier for an adversary to develop an equivalent product than it is to develop equivalent relationships.
For more "businesslike" tech ideas -- where network effects, marketing, positioning, or inter-business relationships are most important -- the business-side execution is more important than the software details.
Of course, your mileage may vary, and most real companies require both technical and business competence to be successful.
The more time you've spent on your code, the harder it is for your competitors to replicate it. As a very rough rule of thumb, the time it takes to build a meaningful competitive advantage is probably approximately equal to the time it takes to get a working prototype, so you can stay at least one major release ahead of your competitors, but this can vary a lot.
Even then, there has to be a really good reason for doing so - everything you agree to is something you have to keep track of and make sure you don't accidentally break at some point in the future.
