In my opinion, the two best aspects of this book are:
a) Unlike some other "Performance" books that I have read, this book focuses on performance and not a million other things. It discusses performance, not DTS, not Security, not Internet, etc. It just talks about performance.
b) With the Acknowledgments section thanking Bill Gates twice, and this book being written by Microsoft insiders, I would have expected lots of hype. Pleasantly suprising, but true, this book has no hype. Just plain facts about performance. Good show.

I did have one small disappointment with this book, though - I was hoping to get more insight into the use of the Query Analyzer execution plan tools. The fact is that Whalen's discussion of this facility is probably the best information that's out there, but it still falls short. If the authors write another edition, we would all benefit if they could work up some detailed examples that explain the various aspects of the execution plan tools. It would be super if they would provide samples that we could download.