Grrr. I typed up a massive post, hit the wrong button and lost it, so please forgive the inelegant summarisation here...
I don't mind a pre-owned book as long as it's not pre-read. I don't sell books as it'd be like throwing away old photographs. The book is a reminder of the connection I had with it and what I've learnt from it. I buy 'new' books, yes, but they're generally three or four pound (my netbook won't let me use a pound sign...) paperback novels from Amazon so I don't tend to break the bank.
Thanks for all your input, everyone. Very insightful.