The primary focus of the book is what evolution (chance mutation + natural selection) is capable of. Instead of turning to theoretical models or logical arguments to analyze the idea, Behe does something much better and more scientific: observation of the changes wrought by evolution in malaria (and in humans related to malaria).
The study begins by observing that most observed changes attributed to evolution are really degenerative changes that provide a competitive edge against something dangerous, like malaria. A key example of this is Sickle Cell anemia, a debilitating blood disease that also decreases susceptibility to malaria (and is likely widespread, especially in malarial zones, for this very reason). Behe compares this to "trench warfare" in which bridges are burned to slow down enemy troops rather than built to advance friendly troops.
Bacterial Window into Epochs
Moving on from this observation, Behe shifts focus from human evolution to malarial evolution to focus on changes in malaria over the course of its battle with humans, especially their advanced medical drugs over the last century. At this point, Behe makes what I believe to be the most important observation of the whole book: that organisms such as bacteria reproduce many times faster than larger creatures, like humans, and therefore should exhibit a level of change akin to millions of years in larger creatures in much shorter periods of time. In a sense, providing a more observable window into the generational effects of evolution. As a result, if evolution were responsible for dramatic changes in organisms, such as bacteria to humans, then we should be able to see some of that power in a relatively short time in bacteria. Unfortunately for philosophical naturalists, as Behe catalogues the actual evolution of malaria in recent times, the changes are neither powerful, nor dramatic.
In conclusion, I found Edge of Evolution to be a highly informative book and highly recommend that others read it.
Of course, there are many who take issue with Behe's book. Perhaps the best critique of Behe's book is from Abbie Smith at the Panda's Thumb, in her guest article ERV & HIV versus Behe. Behe loses.. Unfortunately, as Casey Luskin points out at Evoluiton News & Views at the Discovery Insitute in his article "Pandas Thumb Fails to Refute Michael Behe on HIV Evolution", her key observation that supposedly contradicts a remark Behe made about the evolution of HIV, does not quite fit her critique.
Another interesting critique comes from Nick Matzke at the Panda's Thumb in his article "Of Cilia and Silliness (More on Behe), in which Matzke critiques some of Behe's remarks on cilia construction in a cell, claiming that not all cells that construct cilia do so in the same way as Behe's example.
I found no response to Matzke on Behe's Amazon blog, which deals with quite a few critical reviews of Edge of Evolution.
However, what I find most telling is that almost all the critiques tend to ignore the Bacterial Window argument of Behe that I explained above, chosing as Smith and Matzke did to bicker over some minor details and interpretations of the book rather than dealing with the big picture of Behe's argument, which notes that it is not what we see, but what we don't see in real world observations that matters most.