It's up to you to decide, and that depends on your motivations. But if you don't think you'll be able to make it happen and still want to make the world a better place, probably best to share your idea.
I want to retain credit for the idea. Will a detailed blog post act as copyright of the idea?
If you aren't aiming for profit, want the recognition and want to make the world a better place then perhaps you could patent it and distribute as an open patent?
http://en.wikipedia.org/wiki/Open_patent