Today in Social

Earlier this week, Twitter turned five and today professional social network LinkedIn said it reached 100 million members. Those are two “niche” social networks – niche in that they’re organized around specific functions or contexts – that have grown up. I’m a believer in focused social networks; I don’t think Facebook always delivers context, and there are ways to use it and other marketing techniques to build audiences relatively inexpensively. is relaunching hyperlocal content aggregator EveryBlock as something like a neighborhood social network. Other than enabling Facebook or Twitter log-ins, it doesn’t seem to be leveraging other social networks much. Of course, using open APIs without a negotiated agreement in place carries its own set of risks.