Since pretty much all my books are in the kindle cloud, even those I get from other places, I just take it off the device and it resides in the cloud. I don't keep read books on my device, only unread and not all of those since its so easy to just tap and bring them in. I do have a bunch of collections and one called "read" which everything I finish goes into.
I don't re-read a lot but if I want to, I just find it in the cloud and download it again.
