You know you're down to the final stages of editing when you're obsessing over things like capitalization of bird names (Do I go with the dictionary method or the ornithological method?), the frequency with which certain words or phrases appear in the text, and how to cut at least one more incidence of "he said." (I like to avoid dialogue attributions if at all possible.)
I've also been reading the book backward--starting with the last chapter and working my way to the front. This is a good strategy in the latter stages of editing and proofing, because, typically, the first chapters are the most polished and receive the most attention, seeing as most editing passes start at the front and work toward the end, which means, unless I do it in stages, by the time I reach the final chapters, I'm not nearly as sharp as I was when I started.
There's also the fear of introducing new errors in the process of making revisions, so I tend to operate in a constant state of paranoia at this stage, checking and double checking each change before I move on to the next.
This is also where a second and third pair of eyes comes in handy. At present, those belong to my wife and my oldest daughter, Gretchen (15), an avid reader. I'm currently awaiting her second read before I finally put a bow on this book--hopefully by the end of this week. Stay tuned!