A little while ago I read a blog post by Charles Stross. He ranted a bit about how everybody misunderstands writers, romanticizing the profession without any sense of the reality. In particular he emphasized that he doesn't give a crap about people stealing his ideas. Hell, I know what his idea is for his next Laundry novel: Mild mannered British hacker turned spy finds clues that something horrible and magical is going to destroy the world and foils the evil plot. The idea, as he says, is worth 1% and the other 99% is the grunt work and sweat required to see it through.
I am sure learning that the hard way. I have lots of great ideas for games all the time but actually turning them into a finished product is an incredible amount of work. I am just starting to get people together to playtest the latest iteration of my role playing game (vaguely like Dungeons and Dragons) and it was a rude awakening when I linked them to the documents I had been working on. They found all kinds of vague rules, incomplete ideas and straight out typos. I have been trying to get more stuff written down but just keeping up with all the comments and corrections that came in has been draining away my time far too efficiently.
Book ideas are really worth approximately nothing. They are one of those things that everybody has and which nobody wants - economics might have something to say about the value of such things. The value is in taking an idea and putting in the hundreds or thousands of hours required to expand on it, smoothing it, editing it, and finally getting it out there for people to read. Clearly you aren't going to get far without a good idea but that is like saying you can't start a campfire in the woods without oxygen - certainly true, but lacking oxygen (or a book idea) is never going to be the thing that stops you.
There may be a slowdown in the number of posts I produce over the next little while due to this very thing. It turns out that figuring out some cool mechanics for a RPG is easy and writing an entire 300 page RPG manual is ... quite another.