I've read a couple of books recently which both contained an afterword by the author. Having enjoyed the respective stories - one a novel, the other a memoir - I continued to read the author's comments. Unfortunately, I found this then coloured my enjoyment of the book.
Both authors explained briefly how the book had come about. The one talked of a visit to a town where she heard stories of historical characters which she replicated in her fictional tale. The other author explained how her memoir was untrustworthy due to her poor memory, but also that a number of characters and events she had recorded were completely made up, because she couldn't resist telling a good story.
I felt a bit manipulated, a bit cheated in some way by both of these revelations; one because the fiction was based on fact, the other because the 'facts' were in fact fiction! But it occurred to me that if they had revealed the information at an author event, I think I would have felt differently.
These events are becoming commonplace, but they still appeal because you feel you are being treated to something special, intimate and personal. Sharing comments, almost like a letter to the reader, at the back of the book doesn't work in the same way, for me.