Business ideas are out there, in the real world, you won't find them here (generally). Yes, "scratch your own itch", "do what you know", etc. All of those are true, to a point, and there are plenty of smart people here...some of them are even working on businesses that will be a success (or already are). But, if you just ask a bunch of entrepreneurs, investors, and nerds what they want, it's easy to end up working in the very small and competitive field of "things ten other people are working on, and the entire market is measured in hundreds of dollars".
I'm unfortunately not exaggerating. I've met quite a few people at startup mixers and events and such who were working on clones of things that I'd never even heard of. So not only are they working on something where they have established (by some definition of established) competitors, but it's a field that nobody outside of a tiny set of web 2.0 early adopters has ever even heard about, and only a small segment of those even care about it.
And, of course, I would be remiss in my duties as a curmudgeon, and HN old-timer, if I didn't say this: Ideas are worthless.