All the Time!! I generally end up reading Gone with The Wind once a year. I also re-read To Kill a Mockingbird, North and South plus ensuing sequels, A Prayer for Owen Meany and others over and over again.
I've read most of my collection at least twice due to needs and interests. I love re-reading books. It's like slipping into a familiar world. I always find something new in the text or even read it differently. I look at things from different characters points of view, find new themes or focus on one for that reading. I dunno. My books are like my friends and I like to revisit them every so often.