Here's an interesting question.. because it could happen right here.
We are continuously "inventing" new things with the Arduino. As we all know, what will end up actually selling out there in the world is sometimes purely random- a fad can spring up around almost any product.
The other day I used the TvOut library to make a little video greeting card for my wife. She ended up telling her friends. It was cute, had the potential to become a marketable doohickey, for the sake of the discussion. I put about an half hour into the whole thing. Let's say I turn around, market it, and make a few million riding the fad. Though not legally obligated to do so, I'd probably send the tvout lib author a check, because of the hundreds of hours (unpaid) that have gone into it. If he's been unpaid but I've made millions, I'd feel that I'd been dishonest.
What happens when "free" intellectual property suddenly becomes valuable?