Believe me, writing is a solitary lifestyle. When I'm in the throes of writing, I may not speak to anyone outside of my family for days. If I didn't have pets and kids to feed, I might not go outside of the house for weeks at a time!
A review of a book is an encouraging event. I know that I'm not throwing my stories out into a virtual windstorm of words on the Internet, to fly away to the stars or sink to the black depths of anonymity. Even a short review, on the order of "It was good. I liked it." is a good thing for an author.
So the next time you read a book and you really liked it, please think of the author and post a quick review of the book.