Loved the comment about comfort books. Back in the 70's mine used to be 'pilgrimage' by Zenna Henderson - one of the first what I guess now would be called fantasy books. For many years now it's been Elizabeth Moon's "Deed of Paksenarion" original and now the new series, and of course as the Liaden books. What I love is the way they operate on many levels - each re-read I pick up more bits I missed or didn't have the context to understand last time. They have the emotional warmth and comfort that make them like playing a favorite piece of music. I love hearing some songs over an over - why shouldn't I love reading some books the same way...