It is surprising to know how incentives can change the behaviors of people's every-day lives. This was well explained using the rules of economics in book Freakonomics (Steven D. Levitt and Stephen J. Dubner). Given enough incentives, there are always people willing to take every effort trying to accomplish a task. It's only a question of how much the incentive is and who do you find to provide it. Used well, it's such a powerful concept that can harness the enoumous creativity and energy of millions of people connected through the Internet. Google AdSense is such a good example.
Yahoo Answer was launched today, somewhat late in the game after Google Answer and Amazon Mechanical Turk, but none the less giving some interesting new features. For instance, question prioritization based on popularity, solution voting and credibility mechanism, RSS feed for latest development on a question, etc.
What would make it even better, would be to draw more people to the game, by providing incentives to BOTH people asking questions and the ones who answer them. Where does the incentive come from? Ads eventually, but there could be awards given to the most popular geek who always asks the right question, and the most knowledgable guru who always has the comprehensive answers. Social incentives are also appealing, which may eventually be turned into economic incentives.