Niche social networking sites are sites focused on a specific cause, issue or a topic and target a specific audience. These kind of networking sites offer a more meaningful platform for sharing and offering solutions related to that niche.
This kind of segmentation proves the point that people want to find solutions and share on the internet but want to be away from the meaningless noise and want to find a targeted audience where a meaningful, focused and helpful interaction is possible.
One great example is http://ihadcancer.com an initiative by by Mailet Lopez (a cancer survivor) and the team at Squeaky Wheel Media in New York City. I Had Cancer allows cancer survivors, fighters and those newly diagnosed and their supporters, the friends & families of those affected to connect with one another and share their stories and experience of dealing with the deadly disease.