I don't have much to report at this time; my comments here are mainly to ease the pressure I feel for having started reading this book a few weeks ago but not mentioning it here. The introductory chapter lays a few methodological principles, and the first two chapters survey (i) the interpretation of John 7.53–8.11 and (ii) the referent of καταγράφω [katagraphō; "inscribe, register, write"] and γράφω [graphō; "write"], respectively. I'm reading the third chapter at this point, which discusses the dynamics of reading and writing (two separate and separable skills) in the ancient world.
All of this is in service of a larger argument that the significance of the interpolation of the Pericope Adulterae is that Jesus could write rather than what he wrote. Keith identifies thirty-eight [!!] interpretations of Jesus' writing in John 8.6, 8, and then, of course, the thirty-ninth position, which acknowledges that the text does not communicate—and so is not interested in—what Jesus wrote. So why the double-mention of Jesus writing? In our world, where even first-grade children know how to write letters in the ground, John 8.6, 8 don't make an impressive claim. But, Keith argues, in the first centuries of the church's history, writing had a different significance, and John 8.6, 8 claim that significance for Jesus.
More will come later, especially as I get into Keith's argument proper (rather than the foundational chapters I'm reading now). At $169 not many of you will be able to buy your own copy (though I was able to find a copy online for less than $115!). But I would recommend that everyone interested in John's gospel, the historical Jesus, or media dynamics of the ancient world find a way to get a copy of this book, whether through a local seminary or university library, interlibrary loan at a public library, or, in a few years, when used copies begin to crop up online for less than $50.