If you have over 700 unread books do you ever intend reading them?
When I first got my Kindle I would download loads of free books such as the Classics "because I could" but then realised there was no point if I was never going to read them other than to be able to show off what a big library I had. I've got he complete works of Shakespeare on my Kindle but it has never been opened.
My problem is that I signed up for daily e-mails showing the latest free books and keep downloading a few more each week. I do read as well, but at the moment download more than I read.
I keep expecting the supply of new free books to dry up, but this does not seem to be happening.