After I had answered half of the questions on the QOS exam, I had the feeling I had already failed. Sometimes it's really hard to choose the best answers, especially when all the available answers are wrong (ok, I am exaggerating to get my message across, many options have something wrong in them or the question in itself can be vague)! Poor phrasing exists in many exams (not QOS in particular). When the subject tested is complex in itself, poor phrasing makes things harder. In the second half of the exam I started reading and answering fast, so that the torture would be over equally fast. And yes, it seems that reading less into the questions actually helps! Anyway, I passed, so it seems I can be good at choosing the best wrong answers :-)
The exam certification guide from cisco is a good book for the exam (and for any other qos-related purpose). It makes the exam a fair game (or should I say "class-based weighted fair" game? yet another perspective on the "class-based" terminology :-). I do not support the "read only one book" approach and cisco press has many good qos-related titles. I just say that this book is good (e.g. it has the clearest explanation I ever read on how shaping/policing buckets work). As for the questions on the CD-ROM, I almost stayed away (poor phrasing and errors can be found there too, but another perspective could be that it is good practice for the actual exam :-). I liked the Q&A sections of the book with the open-ended question format. I found those more challenging and helpful.