I will preface this that I have not read this book but I did buy it.
For of those of you who don't know, O'Reilly has a deal of the day with $10 eBooks and there is always good titles to be had. I love holding a book, but for coding the searchability of eBooks is fantastic.
Description
From the creators of Yahoo!'s Design Pattern Library, Designing Social Interfaces provides you with more than 100 patterns, principles, and best practices, along with salient advice for many of the common challenges you'll face when starting a social website. Christian Crumlish and Erin Malone share hard-won insights into what works, what doesn't, and why. You'll learn how to balance opposing factions and grow healthy online communities by co-creating them with your users.
http://oreilly.com/catalog/9780596154936/This is the book of the day and I thought many people here would be interested in it. It's received fantastic reviews on Amazon.