The problem with hunches is that it's incredibly easy to forget them, precisely because they're not fully-baked ideas. You're reading an article, and a little spark of an idea pops into your head, but by the time you've finished the article, you're checking your email, or responding to some urgent request from your colleague, and the next thing you know, you've forgotten the hunch for good. And even the ones that you do manage to retain often don't turn out to be useful to you for months or years, which gives you countless opportunities to lose track of them.
This is why for the past eight years or so I've been maintaining a single document where I keep all my hunches: ideas for articles, speeches, software features, startups, ways of framing a chapter I know I'm going to write, even whole books. I now keep it as a Google document so I can update it from wherever I happen to be. There's no organizing principle to it, no taxonomy--just a chronological list of semi-random ideas that I've managed to capture before I forgot them. I call it the spark file.