One of the most important jobs of marketers is to question assumptions. In his book BrandSimple, Allen P. Adamson talks about Jerry Seinfield's uncanny ability to point out things that don't make sense but are never questioned. For instance he once said "It's amazing that the amount of news that happens in the world every day always just exactly fits the newspaper".
Whynot.net is a website where people can submit ideas that challenge conventional wisdom and the ideas are voted on by the community. Some interesting ideas are break lights that indicate the level of deceleration, a Netflix for books, or different horn sounds for different driving situations. Checking out this site can give marketers ideas to find hidden markets or better serve the needs of customers.