It had to happen eventually. It was only a matter of time before a negative review of Perl Testing: A Developer's Notebook would appear.
As a rebuttal, I could pick apart the reviewer or sing songs about the amount of effort it took to produce the book. Instead, I'll be content knowing that previous generations have already dealt with this, and friends will always be on my side. Please amuse yourself, and read from the bottom review upwards.
... but the font size we actually used is so much more pleasant.
For example, "Object Oriented Perl" is generally held to be a pretty good book, but it also received this review. Likewise, "Perl Best Practices" was getting straight A's from reviewers until this person chimed in.
As long as the negative reviews are just anomalies in the overall trend, you don't need to worry. By and large, the only people who are sufficently motivated to bother writing and posting book reviews are, quite literally, extremists: those folks at either end of the bell curve who either love or loathe your work.
And there will always be those who loathe it. It's impossible to accomplish anything worthwhile without its being misunderstood or simply misliked by someone. It's when everyone is panning your book that you have a real problem.
Great book.