I just passed the 271 with an 899 and the 272 with a 916. This book was my only study resource, but I have been working with the XP OS on-the-job for four years.
The difficulty of the test comes from Microsoft's method of testing. Even though I did very well, I only had "warm fuzzies" with half of the questions as I was taking the test, because they really run your brain through the wringer. So, you must understand why all of the other choices are clearly wrong and only one is right, and this entails knowing the material thoroughly.
The only problems I had with the book are is the horrible amount of typos and strange program behavior with the practice tests, and the lack of anything other than multiple-choice questions.
Other than that, get hands-on training, read this book over and over, and be careful with the wording of questions on the actual exams.