I'm a habitual rereader of fiction. Now that I have a reasonable stock of books in the house, I'm frankly more likely to reread an old book than to pick up a new one. I have some books that I've reread dozens of times in the course of my life.
For me, it's the same as replaying recorded music. Everyone replays favourite music, but some people seem to read novels only once. Apparently the attitude is that they want to be surprised by the story, and after the first time they're not surprised any more.
I read fiction to enjoy the images, the scenes, the characters. On the whole, I feel more comfortable not being surprised by the story; though in any case I'm unlikely to remember all the details of the plot from one reading to another.
The memory of a book that I've read soon fades. My memory of it is like listening to someone whistling a tune, compared with playing the record; or watching a blurred image of disjointed parts of a film dubbed into another language, compared with watching the DVD in English. Every now and then I want to re-experience the original in high fidelity.
When I think of reading a book, I don't usually want to read just any book; more commonly, I want to reread a particular book, because that's what I'm in the mood for. If I pick up some book I haven't read before, I'm unlikely to be in the mood for it; I may not even like it at all.
Nevertheless, I do read new books every now and then, when I feel willing to experiment. It helps if I've read other books by the same author, because then I know roughly what to expect.
If I feel doubtful about reading a new book, I find a good way to evaluate it is to read the beginning, read the end, and dip into the middle—though I've noticed when doing this that it tends to horrify other people.
Um, don't read anything into the date of this post: it's not intended as April foolery.