Justin Williams, on running a niche social platform (in his case, Glassboard, but it applies to App.net and Mlkshk, too, to name just two such services in the news this week):
Finding an audience of people interested in your platform is
challenging. This isn’t Field of Dreams where if you build it
people will magically appear. Once you find that niche of users,
you’ve got to ensure they’re also the type of folks that are
willing to pay to support your platform. If they aren’t, you keep
looking for a niche that will sustain your product.