The question, "Why is the sky blue?" has been asked 889 times on Yahoo Answers, a Q&A site run by Yahoo. "What is your favorite movie?" has been posed 2,203 times. Do users of the free service retain a childlike sense of wonder about the world around them or possess an abiding interest in the film taste of others?

Maybe. It's more likely, though, that they are simply exploiting loopholes and inefficiencies in the "points economy" Yahoo -- in what is becoming a common practice -- has set up to keep the site lively.

A points economy is like a regular economy, except the currency is points, not currency. Even though you can't exchange these points for real-world goods and services, people will still spend enormous amounts of time accumulating them just to beat others in a list of top point-getters, or simply to compete with themselves.

Web sites are taking advantage of this aspect of human psychology and setting up point systems to draw in users to help create "content" for them.

If you're a member of Answers -- total users are in the millions -- you can gain points asking questions, answering questions, and rating the questions and answers of others. The points are good for nothing, save allowing you to move up through the seven levels in the Answerers hierarchy. With each new level, you gain more powers on the site, such as the ability to ask and answer more questions, and thus get more points.

In the real world, incentives can have unintended consequences. Tie executive salary to stock price and you find -- surprise, surprise -- that some of them start cooking the books to get shares up.

Nothing felonious like that happens with the points handed out on Yahoo Answers. But people there and elsewhere try to game the system in other ways.

When Yahoo Answers was launched in December, Answerers were given points for asking a question. After all, what better way to populate the site with interesting questions? The result, though, was a deluge of easy questions, like those involving the color of the sky.

You could also get two points for answering a question, a good thing since the whole premise of the site is to bring askers and answerers together.

But that caused a run of answers along the lines of, "I don't know," or "That's a good question," or even, and more cynically, "Thanks for the two points." The software monitoring things would see that an "answer" had been posted. It didn't have the smarts to understand how bogus the answer really was.

Another way to get points was to help decide which of the several answers to a question was the best answer, which rates the answer higher and gives even more points to the person who answered it. Kevin Cole, a top-rated answerer, said that led to the practice of "speed voting," in which answerers zoomed through the questions as quickly as possibly, not bothering to carefully read the answers but simply selecting the first one that came up.

So why did people bother? One reason is that Yahoo Answers posts lists of the answerers with the most points. The main list, the Leader Board, ranks the site's top Answerers; the current champion, a woman who goes by the handle of "Jane Furrows -- Chavez fan," has more than 118,000 points. But there are also tallies of top point-collectors in each of Answers' subject areas, such as computing or health.

Yumio Saneyoshi, Yahoo's product director for Answers, said his team figured from the very beginning that some users would be using the point system in a way that would make the quality of the site suffer. And so Yahoo has continually fine-tuned the point-award process. For example, it no longer gives out points for asking questions; in fact, now to ask a question, you need to give up points.

Even more-technical steps are being taken. For example, some of the technologies Yahoo uses to find spam emails is being employed to ferret out useless, point-grabbing answers. More adjustments can be expected in future weeks and months, said Mr. Saneyoshi.

Yahoo Answers is by no means the only Web site to have to deal with the vagaries of users in the move to increasing reliance on "user-generated content." Wikipedia, for instance, gives its editors points for making edits to entries. But one result of that is said to be editors making potentially unnecessary minor changes to articles to drive their ratings.

Of course, people participate in Answers for other, more legitimate, reasons, including a simple desire to help people out. I've become something of a fan of the service and have gotten numerous Excel tips from it. (Google's for-pay version, Google Answers, is also worth a look, as it tends to be useful for questions involving serious amounts of research for which you don't mind paying someone.)

Jon Kleinberg, a Cornell University researcher, said the issues involving online reputations and what people will do to advance them are at the intersection of computing science and psychology, and is a hot area for Web watchers.

Online games, with their ranking of top players, are the best-known of all the points economies. With other sites now doing the same thing, let's hope users don't bring smash-mouth-style game talk with them.