Geocities, Friendster, Myspace, Facebook, have only just barely scratched the surface. Everyone is talking about how Facebook has won. They used to say that about Myspace. They sort of said that about Friendster. Geocities was the greatest thing when it appeared. There are infinite ways to connect people, organizations, groups, content, and data. So there are infinite opportunities to provide platforms for connectivity.
Ning didn't work because it was just a blend of Facebook and Myspace applied to smaller niche networks. Creating niche networks is actually a winning idea. Creating niche networks with a template tool is what hindered the winning idea. Templates don't work for communities with divergent tastes. No two communities are alike.
Every niche social circle will have its own cultural set of requirements and idiosyncracies. This will require custom approaches for aspiring tribe leaders to produce. If you're setting up a community, you should focus less on the technical tools available to you and focus more on what the unique needs and wants are of that community. If you're willing to customize the network just to fit that niche, you win.
The trick is in clearly articulating what those differentiated needs and desires are. You have to actually understand the cultural behavior of that tribe and how it differs from every other tribe. Articulate. Not so easy.
What community are you trying to build? Please share so we can point to why your community needs a tribe leader that's willing to sweat the details and make something remarkably unique.