In the old days, that is about fifteen years ago, when you published a book it was hard to know what anyone really thought about it, or even what happened to it once you had signed it off. If you had written a book for a wide audience, you might expect a few reviews in the mags and broadsheets; if it was strictly academic, you might wait two or three years before you saw a review or two in the journals (but by that time you had forgotten what was driving you in the book and were well into the next project). Meanwhile your colleagues would have been generally nice about what you had written (they weren't really likely to assault you over the photocopier with an attack on your reading of Cicero's De Officiis), and you would have had a couple of letters from readers who had either loved or hated what you had written.
It is happily different now. I already shared with blog readers the process of writing my SPQR and got huge amounts of straight constructive criticism and helpful support online (on everything from the title to the structure of Chapter 9 -- or was it 8 -- that bogged me down for weeks). But I hadnt quite realised how that now went on after the book was published. OK this may sound naff, but I have had such fun getting tweets over Christmas from people who were actually starting to read SPQR, with wonderful pics of it among the Xmas presents, with the family dog and so on.