EBay's Founder Meets an Idea That Reminds Him of His Own: "Like eBay, Meetup is turning out to be a bigger idea than it may have appeared at first. The concept is to use the Internet to set up face-to-face meetings among people of like interests, rather than the pseudonymous message boards that are considered communities on the Internet. "

What Mr. Heiferman did not expect was how the Web site would become instrumental in Howard Dean's presidential campaign. In January, Joe Trippi, Dr. Dean's campaign manager, heard that a small group of Dean supporters was arranging get-togethers using the site. Soon he persuaded Meetup to let the campaign formally use the site to organize supporters and to get their e-mail addresses - with permission.

"We hadn't realized that we had created a great user mobilization tool," Mr. Heiferman said.