The best thing about this book is how badly it befuddles reviewers, who become paralyzed by consciousness of their own writing while trying to review it!
It's excellent. He performs linguistic analysis on all kinds of human speech and exchange, from politics to speed-dating to chit chat to King Lear and Robert Browning.
In a nutshell, first person singular denotes: truthfulness, emotional immediacy, and a lower status in interchange. First person plural is more complex but can denote solidarity, haughtiness, or insincerity, depending on usage. Second person pronouns indicate a higher social status. Third person indicates falsehood and an emotional distance.
I heard him give a talk a couple of weeks ago and he used the word "I" a lot. He must be super sincere! (Actually, he puts some of his own emails on the line in the book, to great effect.) This is a fun book!