For those of you looking for any help on statistics, this is NOT the book for you.
For those of you interested in increasing the validity and reliability of your surveys, this is could be the book for you. It does have an effective treatment of writing questions and effective survey design.
If you wish to become an expert in coverage, sample frames, sampling, etc, look elsewhere. That topic gets just 10 pages.
No book can do it all of course but I would have left out some of the "fluff" chapters Dillman included for some discussion of the more technical side of the statistics of analyzing surveys after you have designed them the way he suggests.
As has been pointed out, Dillman does not present as much theoretical material as he might. But, I don't think that that detracts from the strengths of this book. There are other books out there that cover the cognitive and social psychology behind survey answers, and there are other books that give you guidance on the scientific method, experimental design, sampling, etc. (I would recommend Babbie's Practice of Social Research) And Dillman even has a more hands-on book (How to Conduct Your Own Survey) for non-scientists.
But, the real strength of Dillman's book might be how well he instructs on how to put together a great questionnaire - the design, layout, order, question design and implementation.
I find his take on internet surveys to be controversial and a little out-of-date. But, my concerns might be viewed as those of a skeptic - I'm not yet convinced that internet surveys are viable for all that many situations. And, I think Dillman does a good job of laying out some of the challenges and promises of internet surveys.