Every novel is in part the result of decisions the author has made and most of the time, I am sure, those authors have made different decisions than I would have made had I been writing their book. Sometimes this results in my surprise and delight as a writer comes up with something much more cool than I ever would have stumbled into. Most of the time these decisions are invisible to me and I'm just caught up in the narrative.
Sometimes, I find myself thinking along the lines of, "Gosh, I wish he hadn't done that. I hope there isn't going to be a lot more of that as we go along." This is what I think when, for example, the author telegraphs a punch or gives a clumsy explanation for character action or lays out a slab of prose that doesn't flow well with the surrounding prose or just uses a word I dislike (for not all words are created equal, and some words are just ugly in the ear and invoking them destroys the poetry of the passage).
Anyway, this is what I think of as reading with my writerly eye: remaining vigilant to lapses of craft in whatever prose is before me. It's an irritating way to read and frankly it's caused me to read much more slowly than I did in the past. This writerly eye is, I am sure, a by-product of my own writing and revising, because it is the way I read my own works.
This doesn't mean that my inner editor is my primary reader, though. I read first and foremost for pleasure, like any other sane person. Reading just feels good in my head, and I love the simple process of converting graphics into concepts and stories and gosh, but whoever invented the alphabet and writing is my best friend forever. I also read for surprise, for the delight of character and plot and theme and all the other values I have learned to appreciate in fine writing. The writerly eye is more like a separate and parallel process that goes on in the background while I read. Sometimes I think of a narrative as a river through which I am wading upstream and my inner editor is like a hand trailing in the water and sometimes things that don't belong in the river get caught by the fingers of that hand. If it's my own narrative, I pull the seaweed or tin cans or other junk out of the river and throw it to shore and then admire the clean sparkling water flowing around me. If it's someone else's book, the junk remains caught in my hand until--if it's not a well-written book--too much of it collects and I decide to shake all the crap off my fingers and go find a different river to wade.
What I'm doing here, of course, is searching for the proper metaphor for the process of revisions. Some of it is like trailing your hand in a moving river, but some of it is like untangling a knot of string, and some of it is like taking in the waist of a pair of pants and some of it is like patching a hole in a wall and some of it is like planting bulbs in the fall and hoping they'll all bloom beautiful flowers in the spring and some of it, of course, is like trying to decipher Linear B when you have no knowledge of ancient Minoan.