Yahoo Answers from Yahoo Inc. wouldn't exist if it weren't for a volunteer army of devotees willing to provide absolutely everything behind the free, sortable set of questions-and-answers.

That's a lot of work for anybody, let alone someone with absolutely no economic incentive. Yet, six months after its launch, Yahoo Answers now has a sizeable number, about 10 million, of searchable questions-and-answers like this one, the Sunnyvale, Calif. firm announced May 15.

Answers is one of a number of features introduced by Internet search's big three – Google Inc., of Mountain View, Calif., Yahoo, and Microsoft's MSN – that rely on an army of volunteers to do all of the work for them. Some of the new wrinkles have been building for years, and are now incorporated into each of the top three Internet search engines' more general Internet search features.

By doing so, search engines are falling in line with their renewed focus of improving how relevant their search results are. By providing homespun content to search, Yahoo, Microsoft and Google seek to both augment their Web site databases, and differentiate themselves by offering ways of searching the Internet that are unique to each company.

Search engines aren't doing anything new here. But their embrace is of note now because of how Google, Yahoo and MSN are taking the next step in the process by incorporating all this newfound stuff into general search engine results.

Because more than 90 percent of all Internet searches are performed at either these three Internet destination, the audience for the material is going to be significantly expanded.

"For many people, Web search is still difficult to master and find what they're looking for," said Eckart Walther, vice president of products at Yahoo! Search. "By integrating Yahoo! Answers with Web search, Yahoo! is providing a better search experience by making it easier for users to tap into the collective knowledge of people for everyday questions."

Reports from Internet business intelligence firms like HitWise suggest relying on a volunteer army tactic is resonating with users. The firm provides statistics that, taken in one light, show the audience for these features is on the upswing, though still a relatively small percentage of a search engine's overall traffic.

The Hitwise-provided measurement drawn upon for this story involves "vertical" search engines, which in Google's case has been largely how its corralled all the information it gets from users.

In April 2006, 2.67% of Google's downstream traffic went to sites in the Health & Medical category. Yahoo! Search sent 2.43% of its traffic to this category, while MSN Search sent 1.97%.

There's supposedly enormous benefit, and some rather glaring possible problems, as search engines embrace user-generated information.

First, some positives. With a Yahoo Answers-like facet, search engine's discover troves of information topics and Web pages that would otherwise be missed by automated crawlers might have missed.

By having all that on hand, search engines believe they'll maintain and build their audiences. And large audiences clicking on lots of ads is key to how every search engine makes money.

In a telling omission last week at Google Press Day, Google executives recently said that a fifth of all Google inquires are for terms the search engine has never encountered.

Another benefit is the increase in queries that a sharper search engine theoretically attracts. With a larger audience, there's a likelihood more people will click on the ads that accompany search results. Search engines earn most, if not all, of their revenues based on a system of payments by selling advertising.

There's also dangers of using user-generated stuff, as experienced already by Yahoo Answers, and more famously at Wikipedia, the online, communally-created encyclopedia, and Craigslist.

Wikipedia was beset by scandals concerning fake encyclopedia entries, which were used as fodder by some prominent commentators to call in question the integrity of any information available on the 'net,

Meanwhile Craigslist has allegedly been used at times to further criminal enterprises.

It seems the major search engines believe the benefits outweigh the risks, and are forging on.

Aside from Answer, Google's new Google Video search and Google Base classified listings are a big success, say Google executives who do not provide any actual metrics to consider.

Most recently, Google introduced a new feature that looks suspiciously like tagging, a popular way anyone to bring a Web site to the attention of a search engine.

Microsoft is working harder than ever on its own search engine. It's most recent accomplishment was introducing it's own do-it-yourself online advertising feature, an homage of sorts to Google's pioneering AdWords feature.

It also has vowed to focusing much more on search along with other services delivered over the Internet, so it's safe to assume expect more do-it-yourself builds.

All this interest may have played a role in Microsoft's recent deal to buy social-networking maker Wallop, a kind of people finder that, if anything, is the epitomy of this class of Internet feature built off the backs of its users.