The 4-year-old company produces a browser plug-in that recommends popular Web sites to its users based on their stated preferences--such as photography, science or cool gadgets--and the endorsement of others in the Stumbleupon community within those categories. It's like channel surfing with a Web remote that knows what you might like.
The application now has 1 million registered users from Mozilla Firefox, the primary browser it supports, following improvements Stumbleupon made to it in May, according to the company. And next week, Stumbleupon will unveil a public version for Microsoft's Internet Explorer, which commands the majority of the browser market, in the hopes of expanding its membership by the millions.
That way, it will bolster its database of recommended sites, draw more members and sell more of its own highly targeted advertising, said Garrett Camp, chief architect and founder of Stumbleupon.
"We have a new ad system that introduces ads (via Web page) to people when they stumble," said Camp, who compared it to television-style advertising but with a targeted approach to peoples' interests.
All this comes months after several prominent Silicon Valley venture capitalists invested in Stumbleupon, in what was the company's first outside round of funding. Among those investors were Ram Shiram and Rajeev Motwani, two ofbackers, and Ron Conway, an early investor in AskJeeves. Camp would not disclose the amount of angel funding the company raised, but said the figure was in the millions.
The activity plays into an online trend around so-called, or sites that rely on a community of people to populate and drive search results for photos, news, videos and so on. Tagging sites like and Del.ic.ious were among early pioneers for photo and Web site sharing, but a host of dot-coms have emerged to follow suit and mirror the benefits of community-filtered Web search.
Stumbleupon has largely flown under the radar for the last several years, as a profitable but small outfit. In January, the company moved its four employees, including two other founders besides Camp, from headquarters in Calgary, Canada, to San Francisco, where it could be closer to the VC community.
Camp said the company plans to hire sales and support staff to begin selling its own advertising. Right now, it makes money from Google's Adsense ads, or contextually targeted ads, and some ad-free subscriptions members can buy. But its new self-serve advertising engine will allow marketers to pay for placement in its recommendation engine.
The ads, which appear as Web sites, crop up about once for every 20 pages a person views using the Stumbleupon application. Members can give the ads a "thumbs up" or "thumbs down," just like they would any site on the Web.
The application also lets people invite friends to participate, so that they can see what they're interested in, or find people with similar interests.
That way, someone might stumble on a date, too.