I've had it happen once. It was one of my first reviews, and I was delighted beyond words. I certainly don't expect it to happen. It does affect my view of the author, in this case very positively.
I've received many blog comments from authors, and even more emails about my reviews. I have interviewed many of the authors on my internet radio business show, or on my my blog. For some authors, I have reviewed more than one of their books. I follow and am followed on Twitter, and friended on Facedbook, by many of the authors whom I have reviewed and interviewed. They are all such nice people too. :-)
I'm skeptical but I did end up having two authors stop by my blog where they left comments. Of course I wondered why Linda Wisdom would come to my blog but it was nice. I don't think there's anything wrong with it but I really don't go around trashing books either.
A few have stopped by just to say hi and thank me for the review and one emailed me to thank me.
I do post reviews for books I don't enjoy but I always find something positive to say about those books too. So far none of the authors have responded to those.
I did get a response from an author about a published review in a magazine that wasn't favorable and her response was nice response. Other reviewers bashed the book because the character wasn't likeable and she said that I got what she was going for... an unlikeable character. :)