Take a regular blog, and flip it around. What do you get? A reversed blog, of course, where vistors write questions or comments and the author anwers. Sounds stupid, but I think people could get a lot of fun and use out of this. I see this manifesting as a single site with multiple instances (e.g. blogger or livejournal), funded by ads, and configurable to control who can ask questions, who can answer, and so on.
Here are a few examples. A couple's answers their friends' questions. A researcher's or expert's revblog answers questions from others in her field. A CEO's revblog answers his company's employees. Changing the parameters around may allow anybody to ask and answer (a forum) or only the author to ask (a traditional blog), but keeping in the spirit of "questions" and "answers."
For instance, imagine this were a reversed blog where I come up with silly ideas and you tell me if they suck or not. Would that be a good idea?