I've used parts of the book in a class I taught on the Social Web, and yes, I did find it really useful and I think the students did too. This book really is the best one out there summarizing a lot of the experimental scientific research by the research community.

It presents a series of Design Claims, and then backs up those claims by synthesizing the results of previous studies and analyses done by the research community. If you're less interested in the scientific literature, you can just read the Design Claims and still get a lot out of it.

Here is one example Design Claim from the book (you can see it on p29 in Amazon Look Inside feature): Compared to broadcasting requirements for contribution to all community members, asking specific people to make contributions increases the likelihood they will do so.

(Or to operationalize things more: if you want people to do something, don't send a mass email, send the request individually. I've personally found this to be a more effective way to get things done. Remember to only use this power for good, though.)

Also, let me clarify my conflict of interest: I'm a professor at Carnegie Mellon University in the same department as one of the authors (Kraut), who I'm pretty sure the vast majority of people doing scientific research on online communities would say is a clear leader in the field.