As an Internet enterprise, you don't get much more improbable than Kiva.

In a business world where it's all about eyeballs and monetizing what you're showing them, this is an outfit based on strangers lending money to strangers worlds away. And the expectation is that the far-flung strangers will build a better life and pay the money back.

Who would have thought? Who would have thought that, as Kiva approaches its third anniversary, the idea would grow like crazy? Who would have thought that the San Francisco nonprofit with Silicon Valley roots would practically become a household name?

Not Matt Flannery, who with his wife, Jessica, founded Kiva in the fall of 2005. Kiva wasn't supposed to become a media darling, a Web site plugged by Bill Clinton and Oprah.

''We sort of started it as a project or an interesting experiment and that turned into something like a real company,'' Matt Flannery, 31, said. ''That was a big surprise that it became so big so fast and was so real.''

Kiva is real, all right. The Web site features the stories of entrepreneurs — fishermen, farmers, bakers, carpenters, seamstresses, etc. — in developing countries.

Users can choose to lend them as little as $25. The money is funneled through relief and economic development organizations in the entrepreneur's home country. The money is paid back (so far nearly 98 percent of the time). The original lender does not receive interest. The foreign organizations typically do.

Yes, Kiva has grown. A year and a half ago, about 40,000 Web surfers had loaned $3.3 million to 5,000 entrepreneurs. Today Kiva says 333,000 people have made 59,000 loans worth $42 million.

Flannery's message is, in part: Doing good is not easy. Kiva's growth has meant growing pains. He talked about cases in which loans meant for poor people in Africa never made it to the intended borrowers. Times when the

relief organizations Kiva works with were incompetent or dishonest.

''We had this big disastrous fraud on the Web site about a year ago,'' Flannery said.

The local economic development organization in Uganda stole much of the money that was to be loaned, he said. The struggling entrepreneurs never got it, though those who made the initial loans through Kiva received refunds.

Kiva reported the fraud on its site, and Flannery has blogged about Kiva's problems. Improbable, remember?

Flannery, who worked for TiVo before Kiva, holds the title of chief executive. But he lacks the bluster, the spin that often comes with the job in Silicon Valley. He does have a complaint about the media — as many CEOs do. His beef? They're too easy on Kiva.

''My experience is most journalists approach it as a feel-good story,'' he said. Flannery wants it all out there — the stumbles, the inherent difficulties in keeping tabs on far-away relief partners operating in cultures of corruption.

''When things seem perfect,'' he said, ''people are a little skeptical.''

Kiva is trying harder. It does send staffers to check on its foreign middle men and to track down a sample of borrowers to make sure their loans make it to them.

The setbacks have not dimmed Flannery's hopes for Kiva. The organization will soon start making loans in the United States, he said. And someday the Kiva model might lead to better delivery of health care and education where it is needed.

''If we get this right,'' he said, ''there is so much more we could do.''