How to vet Killer Ideas
One thing worth noticing of course is that this relationship is not symmetric: while good ideas are generally spotted by multiple entities, the reverse is not true: just because certain ideas are worked on by many doesn't mean they are good. Good judgment doesn't really grow up in trees, nor do all should-supported containers contain any. Even fools work on things that they consider interesting. That doesn't change the fact that they are fools, and who by definition won't be able to differentiate between good, bad and "whatever" ideas.
I guess one way to look at this is that if an idea is any good, there is or will soon be company in doing it. And if no one is (observed yet) doing it, you should at least be able to get "Ah, but of course!" reaction to it, when presented to skilled practicioners of your art.
Finally: I guess I will also have to side with Paul Graham and disagree with authors of the article itself: I do think ideas, even good ones, are more of a dime-a-dozen variety than otherwise. It may be that the distribution of idea follows some exponential curve (and it certainly is neither flat nor gaussian). But it has always seemed that the difference between success and lack thereof is that of choosing the ideas (and believing and ones chosen), not that of generating them.