When a US Airways plane landed in the Hudson River in January, the first picture appeared on Twitter. In June, Twitter users were mourning Michael Jackson before major news outlets reported his death. And, this month, as much of the nation was riveted by images of a balloon believed to be carrying a 6-year-old boy, every twist and turn was tweeted and retweeted instantaneously, drowning out just about everything else on the site.

As major events unfold, Twitter, Facebook and other similar services are increasingly becoming the nation’s virtual water coolers. They spread information quickly, sometimes before the mass media do, and their ricocheting bursts of text and links become an instant record of Americans’ collective preoccupations.

It’s no wonder, then, that pundits and investors are salivating over the prospect of an effective way to search this information. Twitter, of course, has its own search engine. But others with names like OneRiot, Collecta and Topsy are also vying to become the Google of real-time search.

Not to be outdone, Google and Microsoft reached separate agreements last week to bring Twitter posts to their search engines.

For all the buzz, however, one question remains unanswered: How easily can real-time search turn into real cash?

No one doubts that helping users find fresh, up-to-the-minute content on the Web is valuable. But plenty of other valuable Web services — including content sites, free Web e-mail and social networks — have struggled to find effective business models.

Analysts say Twitter may well find ways other than search to make money from the huge amounts of data that flow through its system.

But Twitter’s chief executive, Evan Williams, said revenue was “not the focus” of its agreements with Google and Microsoft.

What’s more, neither of those companies has immediate plans to put ads on its searches of Twitter, though they may do so later.

And Facebook said last week that it received no money from a separate agreement to make some of its users’ updates available in real time to Microsoft.

“We have no idea how much you can make off of real-time search,” said Danny Sullivan, a veteran search industry analyst and editor of Search Engine Land, an industry blog.

Traditional Web search is a business that practically mints money, and for two reasons.

First, without Google, Yahoo, Bing or Ask, the Web would be an inscrutable jumble of bits. These services are so vital that they are used more than 450 million times a day in the United States alone, according to comScore.

Second, and equally important, search advertising is probably the most effective form of marketing ever invented. Because search queries telegraph a user’s intent with precision, they make it possible to match people with the right ads at the right moment.

As a result, advertisers are willing to pay handsomely to peddle their wares in front of someone who types “iPhone deals” or “Maui hotels” into Google.

For all the billions spent on technologies that track users on the Web so marketers can pinpoint their interests, no other form of online advertising — or offline advertising, for that matter — has come close to matching the effectiveness of search ads.

If real-time search is ever to achieve the same kind of magic, it needs a large volume of queries and the same ability to match users’ intent with ads. Mr. Sullivan said he expected real-time queries to be fewer and more specialized than generic searches.

More specialized, and perhaps not as easily converted into cash. Real-time search is still new, and information about it is hard to come by.

But recent checks suggest that only a small fraction of real-time conversations are clearly commercial. On a recent morning, for instance, only two of the top 10 topics on Twitter — Halloween and MacBook — were commercial. (NYT)