A visionary and optimistic thinker examines the tension between privacy and publicness that is transforming how we form communities, create identities, do business, and live our lives. Thanks to the internet, we now live--more and more--in public. More than 750 million people (and half of all Americans) use Facebook, where we share a billion times a day. The collective voice of Twitter echoes instantly 100 million times daily, from Tahrir Square...