Not that Mary Karr gives a rat's ass (her words) about publicity, but if she is reading this, hi. Send an email. I'd love to hear from you.
For everyone else, I'm reading her book The Art of Memoir as part of my home brew MFA program. To say the least, hearing from the mother hen of memoir how she does it and what she thinks is a good thing. I highly recommend reading the book.
Recently I wrote a post about memoir and narrative nonfiction that talked about the correlation between truth and fact. In short, you are trying to get to a truth with your writing, but in pursuit of that goal you shouldn't invent facts even as you create scenes and dialogue.
And don't think you can hedge on honesty by including some sort of mea culpa at the end or beginning of your book saying you made some portion of your story up in the pursuit of a larger truth. For example, "My mother never actually pointed a gun at me, but I felt as if she were. This and other elements of my story have been created to add to my larger truth and create greater drama for you the reader. Honest, I lied for all the right reasons."
As Karr says, doing this is self-serving and probably more about a nagging conscience because you didn't think your story was good enough or interesting enough or worthy enough, or whatever. It's no different than a lunch counter guy saying, "'I sprinkled a teaspoon of cat shit into your sandwich, but you didn't notice at all.' To my mind, a small bit of cat shit equals a cat shit sandwich."
People don't want to eat your cat shit, even if you tell them you sprinkled some in.