This is a republication, with only slight changes, of the 1993 edition, so the technology and costs are not up to date. But it's not hard to think in terms of digital cameras instead of videotape.
Highly recommended.
The most useful idea I came away with is that testing needs a specific purpose. You can't just test a system's usability; you test, for example, the navigation system or a membership form.
The only flaws here are a couple of omissions. There's no mention of testing web applications, though the principles covered here can be extrapolated to other purposes. And there is no mention of the ultra-cheap guerilla testing tactics. I doubt Dumas and Redish would approve of them, but it would have been very helpful to read about where these alternative methods were effective and not.
This book is a keeper. While my organization will not likely be doing full-blown usability testing for awhile, I'm now more able to evaluate and communicate with third-party testing facilities. And this book will influence all of our other evaluation and assessment testing methods.