Here Comes Everybody: The Power of Organizing Without Organizations, by Clay Shirky (The Penguin Press).

Ever since the first e-mail user clicked "Reply All," the Internet has helped groups form and become powerful. In this book, NYU professor Shirky looks at how people use technology to find others like themselves, how they come to act in concert, and how this phenomenon will change society. Colorful examples range from the cool (Aegisub -- an online group of anime fans who subtitle Japanese cartoons for American audiences) to the stirring (a flash mob in Bulgaria that peacefully defied the president). We've read endless screeds about the Internet disrupting the traditional balance of power between governments and citizens, businesses and consumers. Yes, it's great that now everyone has a voice. But Shirky argues persuasively that the real action is in choirs.