For works of history, an academic press like the two I have worked with (University of South Carolina Press and the University Press of Florida) send the manuscript to someone in the writer's field, someone who should have a good working knowledge of the material and can judge it not only on its style, but on its factual merits, or for the argument it makes. Generally, the readers can choose whether they want their names revealed to the author or whether they would prefer to remain anonymous. I'm very grateful that the two people who read my manuscript weren't secretive. I know both of them and I am very pleased with their selection. They are people I respect and trust, and they have done a fantastic critique of my work.
I suppose every writer is biting his nails while waiting to hear back from the readers. After all, if they say "this really stinks," the author can forget his hopes of being published! And there's always the possibility that they will say "publish but only after extensive revisions." Then it's back to the drawing board.
I was lucky in that both my readers recommended for publication, but they also made extensive comments and suggestions. They pulled out the names of books that I was not familiar with, and that I should consult. They argued for alteration in tone, in places, that I agree will make the work more balanced. One reader sent a long sheet of simple corrections, pointing to places where I forgot to put an "a" or "the" or used the wrong word. That sheet allowed me to insert corrections in less than an hour, a job that might well have taken me days had the reader just said "oh, and correct all the little errors."
I think reading the reader's comments is one of the hardest parts of the process. After all, a manuscript becomes a "baby" who wants her baby to be criticized? But it is very necessary, and it makes every book better. I am extremely indebted to my readers. I've been a reader for several manuscripts, and I know that it is not a job that you do for the money. It can be a real pain, especially if the manuscript is more of a work in progress than a finished product. I should be like those old Saturday Night Live characters and kneel before my readers crying "Not Worthy!" They are certainly essential to this process.
So the next time you read a book and enjoy it, don't just thank the author, thank the readers who came before you.