Steven Kasper, the vice president of marketing for Successful Match, the dating enterprise that started with Millionaire Match, said that 40 sites now comprise his company's network.
As the flagship site, Millionaire Match has about 1 million members (including, at one time, actor Charlie Sheen). But Kasper said a few newer sites include Sober Kiss, for people in recovery programs, and Biker Kiss, for biker singles.
Kasper said that because niche dating sites so closely resemble social networking sites, members develop friendships and communities that seem to last longer than those on mainstream dating sites.
The industry averages about three months per user on a dating site, but he said visitors to his company's sites tend to stay for five or six months.
"What's nice about niche sites is that you develop a community because you focus on a lifestyle or a particular interest," he said. "You find that a lot of people find comfort in surrounding themselves with people in the same situation or who have a similar interest."
Spencer Koppel, founder and owner of Geek 2 Geek, said that as a geek himself, he knew that other geeks needed a bit of a nudge when it came to matters of the heart.
"Because they are introverted, they don't meet other people through more traditional channels, [such as] the bars," he said. "They don't go to those things. They go to comic [conventions], they play online games. They don't have opportunities to meet people in the face to face old way that other people do."
Mainstream sites, such as Match.com, don't really match up geeks with those with whom they'd be most compatible, he said. Geek 2 Geek not only de-emphasizes looks (posting a photo used to be prohibited, but now they're allowed), it prompts users to provide information about their favorite Web sites, gadgets and other more "geeky" topics.
Online Dating Magazine's Tracy said that one of the trends he has seen is an increase in sites for people with sexually transmitted diseases.
When he started his online magazine in 2003, he said dating sites tended to ignore the topic. But now several sites, such as Positive Singles, H-date (for people with herpes) and MPwH.net (Meet People With Herpes), specifically target those who have STDs.
Carter said Positive Singles has grown in membership to 300,000 members since its launch in 2002.
But psychologist Houran said that as with all online dating interactions, niche sites can set users up for disappointment. He said that people who might not ordinarily exaggerate their best qualities offline might inflate their personas online to compete, not deceive.
Someone could present themselves online as being more religious, wealthy or enthusiastic about a particular activity than they are in real life.
But as online dating becomes more sophisticated, tools such as chat rooms, video conferencing and online quizzes give users extra windows into the new people they meet and help them overcome "errors in advertisement," he said.