Language is the ultimate social medium: We don't just communicate to convey information, but also to entertain, to gossip, to console, and much more. Social media data is one of the purest expressions of all of these aspects of language, and often includes additional information about the place, time, and author of a message. This combination has allowed NLP to work on real-life, situated, individual language, rather than on abstract general corpora, and lead it into areas that were previously the sole domain of social sciences. These areas open up a wide range of exciting new applications, but also present a host of new challenges - technically, linguistically, and ethically. In this talk, I will illustrate both opportunities and problems, and end with a number of open questions that I believe will challenge computational social science for the years to come.