Another one: Right now some people are talking about so-called "niche social networks", i.e. concentrate on users within a certain niche, which are automaticall

Another one: Right now some people are talking about so-called "niche social networks", i.e. concentrate on users within a certain niche, which are automatically much more homogeneous in their interests and preferences. HN is actually kind of an example of one. I'd rather have one social network for everyone which automatically sorts the users into niches (clusters), where the same user might fit into multiple niches. The big advantage is that the networking site will find the people with common interests for you instead of the users having to find (and tend to) the adequate niche networking sites!