An interesting look at how social media is changing the way groups form and function. It's full of easy-to-understand, real-world examples. Occasionally the chapters are a bit redundant, but I read it two chapters at a time over the course of several days, so that redundancy helped me keep track of what Shirky was talking about and connected all of his ideas more clearly through the book. The book is written through a sociology lens, but I don't think you need to know anything about sociology to understand his points. All specialized terms are pretty well explained in the book.
I had to read this for school, but it's interesting enough that I could see myself picking it up as a pleasure read.