My problem is my reading taste changes so often so every 6 months or so I have to clean off books I thought I would read soon. I have about 88 books on my Kindle which is way too many I like to keep it around 50.
Thanks to Amazon's Personal Document Cloud I get 5 GB to keep my books available in case I change my mind. There really no reason to keep many books on your Kindle as you can download them whenever needed and unlike Amazon's Archive Items which I couldn't find anything with 5000+ books from them, on the Personal Documents Cloud I put only the books I will read this year. When the first of the year comes. I delete everything and start over.