Pitiless, detailed feedback is the one thing you're sure to get from your publisher (far more so, say, than heaps of money which remain a distant, hypothetical prospect given the current sales of the noir chic titles). It's just as well, because you have little chance of getting it anywhere else.
One of the difficulties of being an unknown author is that, on the whole, the only people who are likely to talk to you about your work are those who know you already. In which case, a full and frank disclosure of what they really thought about it is pretty unlikely. You’ll get the odd enthusiastic endorsement (“loved it!”), much faint and ambiguous praise (“I was pleasantly surprised”), and some clever side-stepping (“not really my kind of thing”). But someone prepared to say “it drags a bit in the middle, and I wish you'd stop rambling on about the history of every building Franck Guerin walks into”? Pretty rare.
Since writing is an endless learning curve (compare, say, the early Rankins with the later ones), critical readers are a lot more useful than indulgent ones. So the next time a friend reveals his or her latest creative project (be it a book, a painting, an hour-long conceptual rock album, ...) then by all means be encouraging, but offer up a little tough love as well.