I had never heard of Yarn Bombing until this book. Otherwise known as knit graffiti, it is an international guerrilla movement that started underground and is now embraced by crochet and knitting artists of all ages stripes. Basically one knits something and then puts it in a public space. For lots of cool examples you can check out Yarnbombing.com.
This book has been everywhere recently...the New York Times, National Post, Good Morning America etc. The author has a new book coming out this fall: Hoopla: The Art of Unexpected Embroidery...it should be just as much fun!