I tend to listen to people's app ideas when their ideas revolve around their life or area of expertise.
For the rest of us, it's easier to start as a competitor in a big market than to envision a latent need and build a product around it. If the app idea has not been implemented before, there's a high chance the founder is having the "invented here" hallucination. I'd try to find a place where the need is obvious and try to build the best product in that category instead of coming up with an ingenious new idea. I believe ideas are overrated (but vision matters).
Steve Jobs take: "I want [Apple] to be much better, I don't care of being different." (Youtube: http://goo.gl/YPQJt)
For the rest of us, it's easier to start as a competitor in a big market than to envision a latent need and build a product around it. If the app idea has not been implemented before, there's a high chance the founder is having the "invented here" hallucination. I'd try to find a place where the need is obvious and try to build the best product in that category instead of coming up with an ingenious new idea. I believe ideas are overrated (but vision matters).
Steve Jobs take: "I want [Apple] to be much better, I don't care of being different." (Youtube: http://goo.gl/YPQJt)