The problem I see facing social networking startups in general is that they are only useful when there are others using it. You have to reach a "critical mass" to be desirable, and getting there is difficult when there are already other bigger social networks with more people. Why would someone join a new social network when they can just join facebook and be connected with more people? The new features would need to be compelling enough for the earliest users to sign up. Because people are intrinsically lazy, those features need be extremely compelling. I think the evolement in this space will stem from new ways that social networking is used rather than simply providing niche slants on existing ideas.