I have a chronic health issue that reduces my reading time and I have so many new books I want to read and not as much time as I'd like for that, so I only very rarely re-read a book. Occasionally I've re-read one I read in high school or something to see if I like it as much now that I'm an adult, or because I don't remember it as well as I'd like to.
I do like the idea of my kids being able to read the books I've read, but honestly I never kept very many books around the house anyway because they take up a lot of space and are clutter. I would have to purchase them again if I didn't have an e-reader, and only have a very slight possibility of having to re-purchase them with an e-reader. I guess I'm willing to take that chance.