I often get people coming to me to help them make an app or game. They send me these NDAs for me to sign. I often feel like this is an unnecessary step. The reason is that the idea is rather pointless it is the execution that is way more important.
I have a lot of ideas and I never make anybody sign an NDA when I tell them my ideas. Chances are my ideas aren't really that original anyway. The problem with ideas is that there is little barrier of entry to actually posses them. You simply have to exist and have an opinion. Executing an idea has many barriers to success. These barriers include: funding, personelle, marketing and a myriad of other reasons.
I find that most people like the idea of just brainstorming and coming up with cool ideas. I love that too. But for whatever reasons in the last couple years, I don't sit down with people to brainstorm unless we have a plan to actually release. To me an idea is nothing without execution.
I have been apart of so many projects that have failed for one reason or another and when that number gets really high you start to feel a certain way about ideas. I know that it is somewhat whimsical to hold your ideas close. But really you shouldn't care that much about your ideas. You should care more about the execution and even then you should care even more about attracting people to your idea.
In the end the only thing that matters is that lots of people are using your product. All of the other factors are irrelevant.