The main thesis of the book is that mass collaboration changes some fundamental aspects of running a business. Three forces have recently come together to create the perfect storm that facilitates Wikinomics: (1) technology (basically, Web 2.0 where anyone can contribute to anything), (2) the Net-Gen -- the generation of people who grew up collaborating (think: kids who view email as a thing only their parents do), and (3) the global economy, where companies are forced to reach out and collaborate to produce additional value (i.e., The World is Flat).
Blog about wikinomics by a computer scientist at Google