To Rent or Not To Rent

that is the question... or at least mine. I never thought of renting books, which is sort of silly since that is sort of what a Library does. I have now rented two books, one EC and one new hardback (to be posted about later). My thought was if I liked them I would buy them. The Ellora's Cave was a sequel and a book I really wanted to read. I went to a ubs I had never been to this weekend and was surprised to see she rented EC and erotica. Her said if she traded them, she would never see them again. So she is building up a library. I thought that was odd, of course I also wanted to buy one of them so that could be why ;). After spending hours there looking through all her books, many of them were older pb and I was in heaven. I decided to rent the EC I wanted to read, turns out to be a good thing because it was boring. So where do you guys sit on 'renting' books? Is that bad? Is it really any different than checking them out of a library?