The book is about the "tipping point", that is, that moment when an idea or social behaviour has reached a level where it "tips" and spreads like crazy.
The book makes sense about how these things happen by using three rules- The Law of the Few, The Stickiness Factor, and the Power of Context. Taking three rules, then, the book uses them to explain seemingly puzzling epidemic situations in society such as teen smoking or bestsellers.
Fun and interesting, if this kind of topic appeals to you, you'll like the book- its well written and an easy read. Other books that might appeal to general interest readers include The Sixty-Second Motivator